You don't need the extra power of the Jot for any HD series sennheiser. At all. Anybody who says that has no idea what they're talking about. You won't even come close to maxing out the power of the m9XX with an HDseries Sennheiser unless you're listening at hearing damaging levels. That being said, I think the Jot is a bit better match with the HD650, especially balanced. Not a huge fan of either with the HD600, as the Jot is too harsh and the m9XX still has the veil. HD800, I think both are good, I prefer the m9XX's smoothness with the HD800 to the Jot, but YMMV. The DAC on the Jot isn't really what I would put in front of a HD800 either. Neither is the perfectly ideal amp for the HD800 though. They're both ***very good*** if you're slowly building an HD800 system piece by piece, but there are better matches out there.