I see I'm late coming to the OP's initial question. If WPS doesn't work for you to connect and get your RP-AC68U set up correctly -- because, for example, you (wisely) turned off WPS in your router due to security concerns, as should be done-- then you need to connect to the RP-AC68U by connecting an Ethernet cable between a computer (preferably one that is not on your network or not connected to anything else wirelessly, such as a laptop with an Ethernet port and the ability to turn off the Wi-Fi). Connect directly from the laptop to the RP-AC68U and then type in a browser window:
http://repeater.asus.com. That will bring up the initial set up window on the RP-AC68U, and from there you can set it up in one of several modes (repeater, media bridge, or one of two different "expressway" modes).
It's actually quite easy to set up if you've ever set up a router in media bridge or repeater mode (as with the RT-AC66's), but there's no documentation which explains this included with the products, and unless you have done this before, it can be quite confusing for some. Asus needs to include proper documentation. But that said, once you know the trick, it's actually very easy to set this thing up initially.
As for it's performance, I've got major gripes. In my environment, the RP-AC68U will hang on solidly to whatever of the three available wireless connections I have it connect to from my RT-AC3200, but in terms of what it outputs, well, that's where the "fun" begins.
If you set up the RP-AC68U in straight "repeater" mode, it wants to connect to both a 2.4Ghz and 5Ghz signal (separately and discretely), and it will then give you the option of "repeating" both of these signals from the router. And as would be expected, it will halve each signal when it is repeated, so that a client device connected to the RP-AC68U in repeater mode will get only half the bandwidth that the RP-AC68U receives from the router. This of course is to be expected.
What I did not expect at all from the RP-AC68U is that when you connect it to both the router's 2.4Ghz and 5Ghz transmissions, that the connection rate for 5Ghz will drop dramatically, and I mean by a YUGE amount.
For example, I set it up, in both "repeater" and "media bridge" modes, using just a single connection to one of my router's two 5Ghz transmits (the AC3200 has two separate 5Ghz radios, one the lower end of the band (e.g., starting at channel 36), and the other at the high end (starting with channel 149). It does not matter which of the two are connected. In my experiments, with the RP-AC sitting about two feet away from the AC3200 (for testing purposes only), the connection rate was 1052Mbps...with occasional drops to 872.5. But the point is, when just connecting a single 5Ghz transmission from the router to the RP-AC68U, whether set as a repeater or bridge, it was receiving the maximum bandwidth from the router. In media bridge there was no drop in bandwidth to devices connected to the RP-AC68U via Ethernet cable (because of course, "media bridge mode" disables and turns off the ability to connect client devices wireless to the RP-AC68U), and in "repeater mode" the re-transmission wirelessly to a client connected to the RP-AC68U cut the bandwidth in half from what the router was transmitting.
But with both radios, 2.4Ghz and 5Ghz on the RP-AC68U connecting to corresponding frequency transmissions from the router, the results were quite bizarre: The 2.4Ghz would connect to the router at close to the maximum rate for 2.4Ghz. at about 285 Mbps (which is close to but hot at the maximum 300Mbps for 2-stream MIMO). But the odd part was what happened to the 5Ghz connection: With a 2.4Ghz connection also made to the router, the 5Ghz would refuse to connect at anything above 385Mbps. This occurred whether the RP-AC68U was set up as a "repeater" or as "media bridge". Either way, 5Ghz took a hit.
In a practical sense, I ran a bunch of speed tests (yes, I know, I should have run something like iperf or really tested bandwidth, and not just internet speed, but I didn't want to spend a ton of time on this). In any event, with both 2.4Ghz and 5Ghz connections between the router and the RP-AC68U, whether in "repeater" mode or "media bridge", the speed test results for devices connected by Ethernet were quite disappointing: Using DSLReports.com's speed test, I only managed around 90Mbps download speed (upload speed, which is 20Mbps from my ISP, was unaffected). My ISP plan is for 300, but I routinely can exceed that (yeah, it's former TimeWarner "Maxx", which is now Charter Spectrum). But the point is that when using the RP-AC68U and setting it up as a "repeater" in the fashion that the firmware seems to "want" (or which is suggested as the "normal" set up by Asus), this device truly sucks.
As a "media bridge" only, and with only one 5ghz connection to the router, the RP-AC68U is great. Get's maximum connection rate, maximum bandwidth and there is no drop at all in download speed testing...at all.
Which I guess works for me, because the only reason I wound up buying the RP-AC68U yesterday was because in Los Angeles we had a power outage with the heavy storm this past week, and when the power came back on it evidently blew out my trusty WD My Net AC Media Bridge that I'd been using for about two years in a downstairs bedroom. The WD media bridge was a nice product, and worked great, also using only a single 802.11 ac 5ghz channel (no 2.4Ghz at all). But when it blew out, I needed a replacement, so it was either get another RT-AC66U and set it up as a media bridge (I have two others on my network now, one of which is a "media bridge" and the other set up as a "repeater", and both work flawlessly). But I figured I'd try something new, so for about the same price as a new AC66, I got the RP-AC68U "Repeater". I thought that this might be a "better" or "new and improved" device, and that I could put it in the location where I'm currently using one of the RT-AC66's (the repeater) and then move the RT-AC66 to the bedroom where it could just be used as media bridge only).
Frankly, I'm thinking of taking the RP-AC68U back because it's actually pretty pricy at $159 for just a "media bridge" and while it does "work', it has none of the versatility of what I'd have with a router being set up as a "media bridge". In other words, because of whatever is wrong with the RP-AC68U's firmware and what it does to connection rates, I think I'd be better off just getting a router to use as a media bridge, and then when or if I need to, I'll be able to repurpose it as a router.
Also tested the "expressway" modes, and frankly, I just don't get what they are trying to do: It has two different "express" settings: 1) You can connect the RP-AC68U to the router's 5ghz radio only, and then that is used for both transmit and back-haul to between the RP-AC68U and your router, but then client devices connecting wirelessly can only connect via 2.4ghz (and thus their max connection rate is a lot lower than what it would be connecting to a 5ghz radio); 2) alternatively, you can do the opposite, which I guess allows for more distance between the router and RP-AC68U using only 2.4Ghz for both transmit and backhaul, and you then connect clients using 5ghz (theoretically giving the client more bandwidth, but of course, you're repeating a connection from 2.4ghz that by definition is likely to be slower than the 5ghz). I didn't have time yet to test these "expressway" options, but either way they seem a bit gimmicky, but who knows? I'm betting though that using both a 2.4Ghz radio and a 5ghz radio in the RP-AC68U will cause the 5ghz to take the same connection rate hit that I saw with "repeater" and "media bridge" modes when connecting to both frequencies of router transmissions.
Don't know what experiences others have had with the RP-AC68U, but mine have been very mixed. It works great as a single-channel media bridge, but that's about it, IMHO.
