IMO the best for those two together is the Headroom Micro Amp + Astrodyne Power Supply if possible. That thing has tons of power and could even handle the HE-6 I think. Probably sweat a little.
There's almost nothing it can't handle. Pretty sure it outputs several hundred Jiggawatts into 32ohm. It's not a weak portable amp. Has a huge brick power supply.
Back years ago I had the Asgard 1 and it was just so-so. Not a fan of it and seemed best for the D2000 and HD-600, but not so much the HD-650. I had both the K601, K702 and HD-650/600.
For some reason I did not have a good experience with the Asgard 2 at all and hated it. I know a lot of people love it. I probably would with a thin/bright headphone like the DT-990 or Grado SR-325i.
Micro is dead neutral, but not cold/analytical. It has a touch of warmth kind of. The closest match i've heard is the iFi ican, but even that is a downgrade.
OK, but too bad the Micro is discontinued. Should be easy to find used though. I paid $350 for mine and if it dies i'm going to pay up to $500 for another. I'd like to get an M-Stage just for comparison.
I bet they're close in sound, but perhaps the M-Stage is very slightly darker/warmer? Micro could probably be found for $250, but it's worth full price.
I think if you want to hear both like their supposed to sound, the Micro is it. The Asgard 2 definitely sounded more colored to me and much warmer for sure. Nothing wrong with that at all.