you can eliminate everything except for a SACD, DVD-Audio's 192kHz stereo portion and currently HD-DVD/BluRay and the AVR. SACD because sony doesn't want to license PC's for playback. DVD-Audio is playable but with 24/96 limitations, again licensing. HD-DVD/BR will be available in the future... but in what terms and what you need to upgrade... that part is uncertain. i've read you need a video card with HDCP ROM built onto the video card, a HD-DVD-ROM or BDRom with AACS chip built and finally a HDCP display. there is already a list of HDCP video card. here's a primer on that:
http://enthusiast.hardocp.com/articl...50aHVzaWFzdA==
BR/HD rom's aren't affordable yet. the selection of HDCP displays are limited. looks like we're heading towards a DRM-limited future.
now, if you feel tah you don't want to play SACD/DVDA ever AND you'll wait until HD/BR is affordable... then you'll replace everything except for AVR. powered speakers are very impractical.
oh if you have VHS tapes... you'll still need a VCR =).
i've been without a dedicated TV for about 4 years now. i use only my HTPC to playback everything except SACD/DVDA (of which i have a standalone) and VHS on VCR.