Hey MangoMonkey,
I think the Micro Stack should work just fine for the 225s. You may find that the HR amps are a little warmer than most other solid state stuff anyway, and turning on the Crossfeed can sometimes help this as well. I would use the medium or low gain setting for the 225s since they wont need as much power.
As for the 650s, I feel like the Micro Amp should be totally capable for those especially in the high gain setting. Are the Micro products you have the current models (post 2007)? The Astrodynes will provide more available current for the amp and DAC so this could help a little, but even in stock form you should have plenty of "headroom" for your 650s. I dont tend to listen very loud so the volume knob stays around 10 O'clock for me on the 650s (in the high gain setting of course). The headphones seem pretty effortless to me at this volume.
Ben Thiede