I looked at both building a MCPC VS purchasing various "MediaPlayer" (very tempted by www.z500series.com
). I went for the MCPC in the end (Win XP with Nero Home) using S/PDIF(will go for HDMI later) for sound to a Yami Amp (V2600) due to the flexibility you get from software. I can play almost anything on the MCPC and away it goes.
If you decide to use the RX-N600 as a combined MediaPlayer / Amp you may be disappointed in the future as its firmware only supports playing MP3, WMA and WAV files from a server over E'Net. So you WILL NOT be able to stream other files types including MPEG's etc over ethernet. You will also still need a PC to stream the data from.
You should not notice a quality difference as both Ethernet and S/PDIF are just a digital transport. You will use either:
1) A PC Software player's CODEC is used to covert MP3's / WMA's to PCM or extract the DD / DTS and transmit these data streams over S/PDIF where the Yami will decode and amplifiy it.
2) The Yami acts as a fancy MP3 player by reading (streaming) the MP3's / WMA's from a network attached drive where it's CODEC does the conversion then amplificaiton.
The sound quality is determined by the "quality"/brand of CODEC used but I doubt you will be also to tell the difference. I've found that compressed music (eg MP3's) sound poor in comparison to the original CD's on the Axioms. I am now using WMA Lossless as my CODEC and can not tell the difference!