Yes, you can setup Lyra network as AP mode, connected to your 87U's LAN. Roaming will work well between lyra nodes. However roaming between Lyra nodes and 87u will be as with any other individual wifi-AP. Your mileage may vary, but in my experience it isn't THAT bad. It depends on the clients. Try all 4 first, then try if disabling wifi on 87U and keeping wifi only on mesh nodes gives better results.