Well there we are, having owned NEITHER of these, I suggest an ART Digital-MPA ($350~), and when you want some cheap flavor for a compressor add an ART PRO VLA ($260~).
The reason for getting the Digital-MPA is that you can go digital in to your m-audio (assuming it has SPDIF), bypassing its pres and conversion, kind'a taking it out of the equation altogether. You get a pre that seems to be well respected, two channels, and you can always add what ever eq or compressor you want down the road. Although I am sure, well one would think the M-Audio Tampa would be a step up as well, and has most of the features of the DMPA plus a compressor which you may want to use for again, flavor.
I am about to upgrade some stuff myself, and the DMPA and VLA are very much on my radar, DMPA cause of the digital out and cause it has loads of gain, something my ribbon likes very much thank you. And the VLA to see what flavor I can get before going into the box, mind you I have a UAD-1 and use its emulation of the 1176 and LA-2A so outboard compression on the low end like this, does have, good maybe even great plugins to live upto. If I get the VLA and it doesn't live up to my plugins I will probably sell it, and then hold out for a real 1176, disstressor, LA-2A etc. which if you haven't checked are a lot of money for a stereo set up.