First; What router?
Second; Dual Band does not equal dual channel (no such thing as dual channel router).
How a router works is like a very old Ethernet Hub in that only two devices can talk to each other at any given moment in time.
When multiple clients are connected, they have to take turns talking to the destinations they're requesting.
With more and more clients added, the responsiveness of the network eventually comes to a crawl because they're using the bandwidth of a single channel.
While all the above is happening, each device is connected to the same channel (one master channel for each band: 2.4GHz or 5GHz) for the duration of the session (until the connection is terminated by the client).
With both 2.4GHz and 5GHz Bands: each can be bonded to 2 Channels which is technically called the channel bandwidth of the connection (20MHz being the basic channel width). With 5GHz AC connections, we can achieve 20MHz, 40MHz and 80MHz channel widths at shorter distances.
Soon with AC3200 class routers we will have 160MHz channel bandwidth (up to 4 channels used simultaneously for each client) in addition to MU-MIMO which will finally get WiFi past the 'wireless Ethernet Hub' limitations that plague all routers up to today.
At least for the download side of the equation (from the router to the clients); these new routers will be able to service up to 4 clients at once with 4 antenna and the spec's call for up to 8 antenna designs (so, 8 clients all downloading at the same instant - which is not what is happening now). We can expect this sometime in 2015 for 8 antenna designs, but the Asus AC2300 4 antenna MU-MIMO router should be available sometime around June of this year.
To summarize; a router can use multiple channels today. This is the channel bandwidth. But these are used simultaneously for each client that supports it (i.e. each client cannot have a channel to itself).
The real jump in throughput for many (> than 10) clients on a single network is coming soon. Asus AC2300 class routers with Quantenna chipsets will be blazing the way forward (we all hope, of course).
The icing on the cake will be RMerlin's support for the new standards.
