don't try to power any mics with the MD it will distort like a 2 dollar whore on dollar day.
While I love that expression, it really depends what mics you're using. Anything with a battery box will block out the md's mic power. Then it's stricly a matter of matching the gain levels to what works best - mic or line in.
Another factor is the bass rolloff on the battery boxes. It will only work if you use mic-in. The input impedance plays a role in determining the rolloff frequency. When you use line-in, the rolloff becomes so low it is inaudible (depending on the input impedance of the line in, it usually ends up being between 1/5 to 1/10 of the mic input). That means a rolloff that starts at 160 Hz on mic-in only starts at 16-32 Hz on line in - inaudible. So if you want to use the battery box rolloff, you must use mic-in, or it won't rolloff.
The last consideration is if the mic itself requires power - only the mic-in provides it. If the mic requires power, while you may get some signal out of it, the mic won't work properly unless powered.
If a taper has a handle on that stuff, there'll be a few less 2 dollar whores in the trading circles
md can make fine recordings. Yes, it's compressed, but I think much of the bad rap is because for $120 or so, md lets anyone get in the game and lots of those tapers aren't into learning. No problem. But if you want to make some good recordings, you have what you need, as long as you're not standing in front of the stacks. Go tape at a few spots around your favortie venue and find the right one (at home, after). You'll know for next time, then let it rip!