Brad,
I agree with Will. I have both the micro and ultra micro stack. The detail (especially in the bass) is much better in the ultra. To me the ultra stack provides a much more organic and pleasant listening experience. Bass is stronger with the ultra. Things such as cymbals have a very nice and natural sounding decay. Soundstage is also excellent. If you can afford it, get the ultra stack. You will not regret it! Do splurge for the power supply upgrade. It is well worth it. There is better control of the sound with the astrodyne power supplies (especially in the lower registers). The ultra stack in my opinion is a fantastic system that for some reason doesn't seem to get much attention and appears to be underrated on these forums. I love my ultra stack paired with my APS re-cabled AKG-702. It is hard for me to even go a single day without listening to music with the ultra stack. For reference, I listen to classical (both chamber and orchestral music), some pop/rock and modern greek artists. Hope this helps!!
Oh yeah, sorry about your wallet!
Tom