i'm using an m audio 410 right now, but another future purchase would be a new interface with more inputs, and the motu 8 pre is at the top of my list. (do you think the pre's on the motu would negate the need to get a separate pre for adding more tube warmth such as the art mpa gold?)
also, do you have any opinions on the studio projects C4's as opposed to the B3's that you recommend for acoustics? any thoughts you have about any of this would be much appreciated! thanks a bunch!
FWIW, I wouldn't worry about tube pre-amps...
Quality tube preamps that have a lot of character start at ~$1500 for two channels.
With lower cost units you're better off with solid state (cleaner/quieter).
The MOTU 8-pre's onboard pre-amps are pretty decent.
They aren't a replacement for high-end preamps (Neve, Focusrite ISA, Avalon, Manley, etc... as they won't add or enhance character) but they're more than capable of capturing good sounding tracks.
The transient response from a small diaphragm mic like the C4 will tend to be more accurate than a large diaphragm mic (less mass to get moving). However, the B3 has a 3 micron diaphragm (instead of the typical 6 micron)... so it responds a bit faster than a typical large diaphragm mic. You generally get more perceived "size" from a large diaphragm mic.
The B3 is sort of a hybrid in that it captures a bit more size/warmth (due to the large diaphragm)... but has transient response that's closer to a small diaphram condenser.
If at all possible, audition both the B3 and C4. The C4 will tend to be brighter with less low end response.
The B3 will be smoother/fuller. The B3 is definitely the more versatile of the two mics.