I'd second the ModWright approach. Dan just got done doing a full blown mod on my Pioneer 38A and the improvement is incredible. Dan does a lot of work on the Sony's so you might also post to his forum located at:
http://www.harmonicdiscord.com/forums/viewforum.php?forum=4&20
to get a few more opinions and some feedback on how the modifications stack up against an outboard DAC.
http://www.harmonicdiscord.com/forums/viewforum.php?forum=4&20
to get a few more opinions and some feedback on how the modifications stack up against an outboard DAC.