You could also buy the Bottlehead Quickie and a solid state amp as long as your DAC is separate from the amp.
That way you can flip between SS and tube tone when you feel like it.
If I remember the BH Quickie expands the soundstage according to one 500 user who said it was great in his set-up.
T-amps are under-rated for powering HFM cans with one extremely techie member on here (Robrob) saying his was close to his TOTL Schitt amp. So if you can get your cables balanced you'd have more than enough juice in reserve for your 400's if you went that route of tubie and SS speaker amp.
Edited by Lohb - 4/16/14 at 10:11pm