Ya, not sure if COVR worth with other DIR routers. I know the 2660 has a MESH option. I've not tried it. My 2660 works with my DAP-1820.
If you have COVR, it's easy to add additional LAN ports with a external Gb LAN switch. Like D-Links DGS-105 or 108 series or DGS-1100. You can use other non d-Link Mfr switches as well. I have a 24 port HP pro curve switch on my network.