If I am hooking up 9 rooms plus a modem should I install a amplifier?
Yes youll probably going to need one. Make sure the modem goes before the amp. I'd go with a 3 way splittler with the 3.5 leg going to amp feeding a 8 way. So the modem & 1 TV are off the 7 legs of the 3 way.
It depends on the signal levels you are getting in each room. I have 8 jacks in my house & have acceptable signal levels without an amp.
See this previous thread in the Cable TV forum for info on amps: »[DVR] Which AMP to use
Especially take note of the last post in that thread.
You cold get an amp with upstream boosting too, I have plugged modems on the other ends and they work fine.»www.amazon.com/gp/product/B003UH···_s00_i00works great