I'm using the Japanese Bakoon - pretty amazing soundstage almost makes my TH900 HD800esq very smooth amp very musical.
I think it's best h/p amp I have used with TH900.
If th TH600 is 8-10% less than TH900 in terms of sonic abilities as stated by forum members the the imaging will be excellent with the Bakoon
Is that the HDA-5210 MK3? There's quite a bit of confusion surrounding the Bakoon amps.