you might want to post in the "rack" section, but I'll give it shot - I don't know the tascam unit, so I bet there are some inaccuracies in what I'm going to say:
1) connection between DMPA and Tascam -
a) you can attempt a digital connection, but it might not work - you need a coax s/pdif cable - like these:
http://www.bhphotovideo.com/c/buy/Coaxial-S-PDIF-Cables/ci/4199/N/4294544135 (shorter is better, and as long as it's rated for S/PDIF, you don't need a fancy monster cable, imo - it's a digital connection, after all - either works or doesn't) and you connect the "out" on the DMPA to the "in" on the tascam. I do this with my interface, but to make it work, I had to use an external word clock to synch the two devices, and it doesn't look like the tascam supports a word clock connection, so you could be screwed - S/PDIF is supposed to include a clock signal (at least on the fiber-optic cable), but it didn't work for me. Try setting the clock speed on DMPA to what you want on the S/PDIF side and cross your fingers, set the dither to 24 bit (I think) and the ADAT/S/PDIF switch to S/PDIF - turn down your monitors before testing - worst case is you'll have very loud clicks and pops
b) if that doesn't work, just use the analog outs from the DMPA and connect them to the analog ins on the tascam - much easier
- I guess you need 1/4 inch trs cables for that
2) DMPA settings - make sure that you know which of the two sides you have the mic plugged into (left or right) - make sure phantom power (48v) is turned on for the mic you have. Also, make sure the tube output button is pushed in and also the plate voltage is set to "high" (not sure why they even have a "low" setting). To begin with, leave the 20db gain switch off. Make sure that the hpf knob is all the way down, as well as the input gain, the digital level, and analog output. Turn the input impedance knob all the way up or almost all the way up.
to test, keep your monitors set low (or better, off, and use headphones, and keep those set low) - first turn up either the digital level (if you're going digital) or analog output (if you're going analog) - keep going and stop if you hear too much hissing - you'll have to get a feel for that. Theoretically, these should be all the way up, and you should only turn them down if you want to "drive" the circuitry in the DMPA and then attenuate the signal so you don't overload the Tascam - in practice, though, my digital level is usually at about the halfway mark - I don't use the analog out.
Next, turn up the input gain slowly, while testing the mic. If there's too much hiss, try turning down the input impedance some. If there's not enough gain, try the _20db boost, but first turn down the input gain all the way before turning it on, then creep it back up. The way the Input gain knob works on the DMPA, you get a big jump in gain at around 3 o'clock (I think that's right) - it's to be expected, and you just have to work with it.
In the end, you want the input impedance up as high as it will go without an unacceptable amount of noise. Also remember that you really don't want a very hot signal going into Logic - you can boost the signal with the "gain" plugin later - for now, you want to leave lots of headroom.
If the whole unit is too hissy, you might want to change out the tubes for quieter ones. Actually, if you have the stock tubes, you *probably* want to change them out anyway, because they sound bad in most of the units we hear about - kind of shrill and phasy (and hissy/noisy) - certainly true with mine. If you're interested in swapping the tubes, do some searches here and you'll find plenty of info
