Indeed, but a PC that is capable of playing most of the current crop of games is also going to be a fairly big, heavy, noisy and hot beast.
Ultimately, get what can do what you want it to, but also remember where it has to live
Audio-wise, you aren't going to need a lot of volume and a home theatre amp is going to be waaay overkill I'd have thought. If you go down the PC route then why not get one with built in support for HD audio (i.e. a 5.1 or better still a 7.1) with the appropriate number of audio outs. You could then feed these to small self-powered speakers. OK it's never going to be great but then it's stuck in a boat, hardly the pinnacle of audio chambers!