Hi Scy -
I have the rebranded Shure, and was having the same problems feeding into my MR1. I had gain set at about zero, and was still getting a very strong signal into the MR1 from my AKG 460's and 391's. I ended up putting a 20db pad between the mics and the Shure, and another 20 db pad between the Shure and the MR1. As many have commented, the MixPre is for lower volume situations, and expects to be able to pump out a pretty hot, full professional line signal which can easily obverload the max +6 db signal the MR1 will take.
I haven't tested it live in a venue, but initally the result seems to be a significant improvement. I run the gain knobs at about 50-60% of the way to maxiumum, and I think that using a larger amount of the gain is giving me a better ratio of signal to noise. With the gain turned all the way down, I always wondered if the noise floor inherent in the preamp's output was too close to the insanely low level of signal coming out.
FYI, my pads are fixed 20db pads, not the adjustable, but the adjustible seem like they would be more convenient. It helps that the mics have a built-in -10db pad if things get too hot.
Good luck!
Mike