If you want world-class results, rivaling your vinyl, then jitter is the primary thing to tackle, both in ripping and playback.
1) Record hi-resolution digital from LPs - you need a GOOD A/D converter - the Ayre QA9 is the only choice IMO
2) Play CDs (Redbook, SACDs) - A CD transport, coax digital cable and a good DAC. The CD transport should be based on a high-speed CDROM reader with clocking from memory for lowest jitter. There is one from PSAudio and one from Parasound and others.
3) Play hi-resolution digital files from a computer through my stereo - the best result with ANY DAC is to use an outboard USB converter with high quality power supply to achieve the lowest jitter and then feed a good DAC with a high-quality digital coax cable. Most DACs with built-in USB interfaces will likely disappoint you.
Good DACs are not cheap. If you want the best performance on a budget, start with a NOS (non-oversampling DAC) like the Metrum Octave, Metrum Hex or Chinese DACs like the Chamelion. These will not match your vinyl probably, but will not be harsh sounding either. Good non-NOS DACs that will do hi-res start at $4-5K IME.
To get stellar results, the the best server currently is a Mac Mini with Amarra playback software on it. If you are not used to Mac, it has gotten very close to the PC for usability, so fairly easy to pick-up. I recommend the Oct 2009 mini combined with a 5 amp Hynes power supply. The hard disk should be replaced with a solid-state-disk for around $150 and the memory upgraded to 8 gigs. The whole server with Amarra will run about $800.
Other recommendations:
http://www.empiricalaudio.com/computer-audio/
http://www.empiricalaudio.com/computer-audio/recommended-systems
Steve N.
Empirical Audio