I have not done or heard a straight comparison, but I used to run a modSBM-1 and currently have a MT and I can say without hesitation that the modSBM-1 blows away the A/D in the MT. I really do not like the MT's A/D; it sounds harsh to my ears, while the modSBM-1 was among the best I ever heard from a 16 bit unit. The Apogee units sounded better to me, but I would not purchase one right now due to the word clock issues; the SBM is a much more reliable device at this point and thus makes a better purchase.
I think that you may want to think about whether to go to 24 bit or stick to 16 bit sound. I really like 24 bit recordings better; they have a much greater sense of space and staging, but this is just how I hear things. I don't know of any, nor do I run any 24 bit A/D converters that would be the same price as a modSBM-1, but maybe some others on the board do.
One drawback to putting the modSBM-1 in front of the MT is that you will not be able to record in 24 bit mode because the SBM is only a 16 bit device. Just something to consider.