I just move from 563 to 578 this weekend.
This is my change log:
1 - I can't notice any degradation of sound on DVD-A neither on SACD
2 - The 578 can play DiVx
3 - The new one doesn't have volume control on the 5.1 analog outs
4 - Poor MP3 GUI on the 578
5 - 578 if faster than 563 to load all kinds of media
6 - The 578 can play WMA, 563 don't
7 - I think that 563 had more bass, and the 578 sound is more clean on DVD-A
I think that 578 is a totally new player that only shares the same from panel layout from the others Pionner DVDs. All conectors in the back panel are in different positions.