So I've tried using my SM 58; connecting it to a 1/4" converter and plugging it into the 'Line In' input of the Micro BR, then singing. The resulting output volume is obscenely low. I've sung so loudly that it's borderline shouting. I've set the input volume to the maximum, and I meddled the effect patch so that the input and output gains were at maximum. All I got was a loud buzz and incredibly soft vocals.

Any suggestions? Also, I've pretty much had the same volume problem when using the Toneport GX. The mic volume is frustratingly low.
If I'm not mistaken, the GX doesn't have a mic preamp. The 57 and 58 are notorious for needing a fair bit of gain to drive them properly. That's probably why you've been getting poor results from your BR and GX - because they don't have the preamps required to get the best out of your mic.

Just use the built in mic for vocals with the BR. I thought it was fairly decent when I had one. As for the 58, you'll probably be best getting a better interface than the GX to use it with, one with a mic preamp.

Maybe you could buy a preamp and put in between the mic and BR...
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Yes you'll definitely need a preamp with that setup. You can buy one from Musicians Friend, they range from $30 to thousands.
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