@ ssddx - I think the OP is stating that since Comcast started encrypting their non-basic channels, s/he's been losing the channels they want "(A&E, FSN Detroit, ESPN, stuff like that)". That would be due to the fact that there is no Set Top Box for the TV upstairs.
@ xmartyx - The simple answer is no, you have to pay the extra $10/month to Comcast for the third set top box. The long answer is "Maybe" and that will take probably a lot of phone calls with Comcast just to make sure that you understand all of the specifications you need in a purchased set top box *and* get assurances from Comcast that once you purchase and connect a set top box, they'll activate it. If they decline to activate your own set top box for any reason, you just bought a paper weight.