Hi dtox.. longtime no see!
K790i is based on walkman platform hence there is slight or no difference in audio quality. I think its an excellent buy at 11k or so. Plus you being the " SE mod guy" its suits you perfectly
5610 is more stylish. As someone said, audio quality is subjective and to my ears 5310 sound better than 5610! (Plz don't start a war on this!). Unfortunately what lets both down is the crap camera.