Wired/Wireless Combo

Hi, I hope I don't make this too confusing. So, in room A, I have the cable modem (with only one output LAN port). I also have my TV and a DVR in the same room, and want to hook them up to the internet. In Room B, is where I have my router, that will give wireless to the rest of the house. I needed to move the router to that other room for total coverage. 1. Optimally, I would like to add a LAN switch right after the Cable modem and hook into the Room A items. Then another port I will send to my Router and thus make it wireless for the rest of the house. Room A stuff does not need to be inside my home network (the wireless side), so not concerned about that. I have been reading and they said its not a good idea to put a switch between the modem and the router, as it might get confused. Or I can insert the switch on the output of the router and just run LAN cables from the switch in room B to Room A tv and DVR. I don't want to use the electric outlet LAN adapters. Which would be best? Like I said best is to insert the switch between the output of the modem and the input of the router. Everything is Gigabit. Thanks in advance! Curt