Up and running with the new equipment.
Macbook pro -> toslink -> uber Bifrost -> HDVA600 -> CH800S -> HD800.
Great sound right out of the box. Very revealing of the instruments. Soundstage is impressive. Plenty of bass and the mids are super.
I tested the rig with the LCD-X too and they sound great with the gain on the HDVA600 turned down to the minimum.
Thanks, all, for your help -