I have the MJ and my good friend has the BHC.
In terms of musicality and euphonic sound... the BHC crack still wins out with unreal synergy... superior in all tonal sense for jazz, vocals, pop, etc. and plays to the HD 650's inherent strengths.
The MJ is indeed the best in the Schiit lineup for me... and yes... it does drive the HD650 with a level of authority that keeps it ohhhhh soooo clean. It is very resolving, and most accurate sounding setup for the 650 that I have heard. If there are those out there who want more clarity and less "veil" and "coloured" sound... the MJ + Gungnir does a very solid job. Going fully balanced though, the soundstage and imaging goes to a whole new level IMHO... it makes listening to more grand orchestral pieces like Beethoven's 5th and 6th a complete treat... it really brings out the sense of being in the concert hall.
With all the said... I am EAGERLY waiting for a group buy site (who's name I think I'm not allowed to mention here) to have the BHC + speedball available @ discount. When it does, you can be SURE that I will jump on that so I have the best of both worlds for the HD 650.