I've heard mention in the comparisons between new/old driver versions that the newer 580/600/650s are all much easier to drive, even if there's contention about whether they sound any different from the old ones. A/B'ing mad dogs (~50 ohm) vs. HD650s (purportedly 320 ohm) seems to confirm this as I feel volumes are dead even between the two. Would this be a concern if I were considering an OTL tube amp like valhalla/crack, seeing as they're supposed to be such poor matches with low impedance phones?
I know those two amps have been recommended a ton for HD650, but I wonder if many of these recommendations have been made specifically with regards to the new driver versions.