Enhanced sound?
I've not seen anything that says the audio on cable, or sat, are high definition... only on discs can one find the higher res audio. Blue Ray, older HD might, but I doubt it. And there's the advent of transporting HDD based music in high res files from a pc/server into a HT rig.
In fact I'm not so sure that even the HD video being sent over cable or sat, is past the 720p info currently. Some boxes allow for 1080i though, so it's a 'pick 'em' at that point with some preferring progressive over interlaced... an aspect of HD is line for line all at one time... progressive video info.
I think the limitations are simple bandwidth constraints. 1080p + 24/192 x 8, will eat up a lot of the supply pipe.
Don't be confused with terms cable likes to throw around... High Definition pertains to video, high Resolution pertains to audio. Blue Ray is your ticket for both at the same time.... here in the U.S.
Got a budget in place?
I'd say 120wpc into 8 ohms, or better should serve there.
Separates? Receiver? Onkyo, Dennon, Marantz, etc all make good ones. Sony too for that matter. $600 1000, should get you a pretty good receiver in the preowned mkt... that has HDMI 1.3a. HDMI 1.3a is a very good thing to ensure you wind up with. For new, figure 900 - 1800. Separates will run more of course.
Canare 4S11 spool speaker wire will do a good job too and not break the bank.
Room size will say much about the sub you'll want to add. HSU & SVS among others are good places to begin looking.
Good listening