Just because it has a TA
connector doesn't mean things are interchangeable. Most
Shure body packs output 5V
bias power. The MX391 wants to see somewhere between 11-52Vdc according to its spec sheet, so mic
bias alone won't
power it, you will need some sort of external
phantom power supply. You'll want an
XLR to TA wired for
dynamic mic (Hot Pin 3,
Ground Pin 1, same on
XLR and TA4F), run into a
phantom power supply, out to your mic.
Even the AT871 wants 9V
Bias Power at minimum, the reason it works on your AT belt packs is because some of those give out up to 11.5Vdc -- again, connectors connect, nothing more, doesn't mean they do the same things internally.