Justin, my personal theory is that human hearing is not getting any better, not enough time has gone by for our auditory perception to evolve beyond where it's at now.
But audio technology has developed to a point now where I don't think it can get any better, other than non natural sound, surround ect.
What I have noticed is that it has made the turn full circle and is now heading back in the other direction. People don't care about fidelity anymore, mp3 is the norm.
A lot of production is going for a grainy, non detailed sound, some John Mayher stuff sounds like that to me. So I still think a hit can be tracked on an adat, and maybe even a 4 track cassette player.
I had a singer in here, had her own band, toured on the "Peaches and Herb" last year, remember "reunited"? She was the new Peaches. Anyway we tracked 24 songs (for an agency) to downloaded MP3 versions (Karioke), most sounded pretty bad, the MP3s, but she could not tell and made no difference to her.
So, I can honestly say that to me it does not matter what new converter comes out, or pre amp or anything, it's over.