Digital media server/players for a Skeptic?

I have all my music on a windows pc running itunes.  I mainly use airplay to listen on my apple TV connected to my receiver.  I then often use an ipad to change tunes and such.  My receiver also has airplay and sometimes I use that but can't really tell any difference between it and itunes. 

I do hate itunes though.  Slow, crashes a lot, hard to really manage a lot of files (~35,000 songs).  My music is mostly coded using whatever the highest rates of MP3 are. VBR 320 or something.  And I've given up on the various tools that try to fill in missing tags.

My current system is Ascend Sierra 2 mains, orb sides, Marantz 5009 receiver, Rega TT, nad preamp, nad cd player.  I will probably upgrade the marantz next year.  Don't even ask me about my interconnects.  I am not a belieber in the audio hoodoo. I use good cheap wire and cables.

So how much sound quality difference and usability/convenience do some of these music servers, decoders, whatever the heck they are really offer over using apple TV? 

Thx!