I used to do sound restoration for a living so it was essential to get good stuff, though I didn't kill myself - it paid off, as. honestly, I consider myself better at sound restoration than anyone else I've heard; it's because I have a good, sold audio chain, good converters, and the world's best speakers, no kidding, a pair of Brysyton's Lab's that cost me more than I have ever spent on any other piece of equipment - not to mention ears that I trust more than anyone else's - I know it sounds arrogant, but in the days when I did a lot of custom sound work (putting LPs and tapes onto CDRs) I was called the best in the business - also helps, in your system, to have a good (and preferably digital) eq - essentially I like analog sources that are well re-mastered with digital techniques -
but I repeat - most important thing: YOUR SPEAKERS! Crappy speakers make crappy sound which is why there is so much crappy sound in the world -
also: Learn how to EQ and you will be able to listen to a lot of stuff as it should have been mastered (a few well-chosen frequency boost makes ALL the difference - it wasn't for nothing that Al Haig named one of his songs "Earless Engineering.")