Addressing the digital question only (amps & room treatments are worthy side topics, as others noted)--I found a very large increase in my appreciation of digital audio just by ditching delta-sigma DACs and going to multibit, especially NOS (non-oversampling) multibit. After doing so, all that subtle harshness, hyped transients, and shallow 2D note bodies are pretty much gone; music has its true weight & impact restored. The cheapest really good sounding NOS DAC I know of is the Audio GD R2R 11, a combination unit (DAC + headphone amp). You can easily use it as an amp only, however, using USB input/RCA output pair to preamp/amp. You'd get one of the most praised inexpensive NOS DACs around + a bonus (and rather good/strong) headphone amp--for <$300. Just sayin'...
