I'll just say that there is quite a bit of my money in my main sound system. It's pretty much equivalent to a club system, in that I've spent more time ensuring a good loud sound, than ultra ultra clear quiet time. Right now I'm probably pretty much amp limited, but decent amps tend to run a pretty penny for high end.
EQ's are an important part of my system at the moment, but I've been looking closely at DSP's which are totally cool, but again cost way more than necessary. As far as PC sound goes most good new DSP's can be used to properly route multi channel signals from a PC to an ultra fine sound system.
I have to have my PC hooked up to something thumping for MP3's, but I still say the best use of a good sound system is for games though. Good games are so much cooler with good sound IMO. I bet it won't be too far in the future until my TV and DVD get merged in there too, probably when I can get a good DSP.