If you insist on reaching for the higher highs, there are better things for both recording (Type-R Sonys, H.D.E.S. Panasonics) and playback (the 831), IMHO.
But the difference between those and the 770 may not be significant enough to justify what you have to do to achieve them. Let me elaborate:
Let's say, I buy a Sony 470 deck for recording, and a used 831 for listening. This is one of the really cool, sweet setups in my head. Compared to buying just the 770,
(a) I'll have to get a home deck at $150-200 extra, and
(b) I'll have to live with a piece of used machinery, I don't know how much life the pickup's got left, and
(c) I won't have the flexibility of MDLP or Group Mode - they could come in handy some day.
So life is easier and simpler if you just buy a 770 for all recording and playback. Its playback quality isn't as good as the 831, but isn't very far off either.
I wouldn't use Sharp's ATRAC to record, but not because it's fatally flawed; just that Sony and Panasonic's new versions do an even sweeter job.
Sharp's remote isn't the greatest, but I think it's still nicer than Sony's stick remote. Sony will not have an ergonomic piece of s**t until they realize how hard it is to twist, or hold down buttons for two seconds on the go. :P
Hope I've been helpful in this thread so far, and remember I haven't auditioned the Sony R909.