Well after 2 weeks and lots of burn in a few lasting thoughts:
On the downside:
Way too much gain, even with -10db attenuators its LOUD ... Going to borrow/buy a sound meter to record the levels, but in comparison with my other amps, min. on the 332S is about 75% max. on my Jade.
Hum ... this started out quite noisey, and has dropped off quite alot, but its ever present, and if you turn off the power the hum dissapears before the music does - so its looking like is a circuit design and not a tube/burn in issue. The hum isn't noticable when music is playing, and to give a fair comparison - listening to an orchestra you can often hear (with cans) various rustling, coughing, scraping of chairs etc - well the hum level is at that level, you can hear it, but its not in your face. Can I live with it ... well....
And the upside:
Sound :- well it just sound gorgeous, really full rich tone with the HD-650's. You can hear that wonderful full base, tight, resonant, full of life; and the mids and highs are clear and crisp. All the microdetails are present, lots of hidden sounds etc just pop out unexpected at you; the soundstage is just that little bit fuller than the Jade for example, there is more room around instruments, everything is just that little bit more in focus. You can follow an instrument easily, it never gets congested. I've switched back and forth with the 332S and the Jade and it just has that little something extra.
In balance - do the pros outweigh the cons?
Very tricky .. The black background of the Jade is great, it allows you to forget about the amp/headphones and just enjoy the music, that little hum on the 332S just stops you short of forgetting the gear.. maybe its because my mind is trying to trick me; is the hum gone? ah no.. there it is!