How do i get more channels on comcast?

I recently got comcast cable & the tv in my living room has a cable box (w/on-Demand). I decided to get a splitter and run a cable from my living room to my bedroom, thinking I would just be able to get the basic channels. However, all I get are like cbs, nbc, abc, & the cw. Is there a way to get more channels? All I want are the basics like i have in my living room (tbs, mtv, espn, etc). I don't really want to get another box if that's what I have to do.