[diggrd]

I always went mic > batterybox w/rolloff > line-in on my MD. I started this after my first mic-in attempt was a disaster of clipped and distorted noise.

From what I'm reading the CSB's may have low sensitivity and need loud source to really sound loud. The line-in may not be the solution in your case.

What I'm confused about is the fact that you are getting a low recording volume so the thing distorting may be whatever playback amplifier you are cranking up to compensate.

I would try recording something at a much higher level and see how it sounds. I don't think the -20 is going to do it I would try getting as close to 0 as possible and compare the results if it's better even if clipped here and there then just work down a little at a time till you have the highest level without clipping.