I bought AD797BR 3 weeks ago, and can say, that it's a good upgrade. Sound goes more aggresive, but there is a lot bigger soundstage, good clarity and overall it's better. Low impendance headphone is more sensitive to that op amp switching, that high impendance headphone. But now i still waiting for THS4032 abd LME49990 just for comparison. Think that THS4032 is good upgrade like AD797BR, maybe better (too many good feedbacks here), don't know, will see :) All opamp were purchased on ebay and were delivered to (soviet) Russia.
Tested on HD650 and CAL!. Wish you make a right decision :)