I'm looking at these two preamps as well.
Any further input on the preamp sound quality? I listening to a youtube comparison, though through laptop speakers, a huge difference... not necessarily one better than the other, but the Mixpre-D sounded like the FP24 (a preamp I used for a year). The Mixpre/FP24 is a good preamp, maybe a little too much gain for small loud rooms, but very good.
USBPre2 Pro's - more I/O's that can be used simultaneously, better computer audio monitoring/playback
USBPre2 Con's - no internal battery, larger than the Mixpre-D, but still can run on USB battery supply for standalone use.
Mixpre-D Pro's - internal AA battery power supply, smaller than the USBPre2/compact
Price is about the same. So it comes down to the preamps. Transistors/Transformers - Is one better than the other, qualities? what is your preference?