As far as i know, i haven't seen anything directly "replacing" the N707. You can't even purchase a 707 on the Sony website. I think the 810 has am/fm/tv tuner. Not something i really would want in a minidisc player. Who needs the radio anyway? Now if i could copy songs directly from the radio, that would be something i'd be interested in .
I think the 707 is the best model out there. The only complaints i've seen about it, was the software. According to this site though, theres plenty of other software options to choose from. If i find anything out, i'll be sure to post it here.
Deadguy