Another thought, you probably need a mic pre-amp to go into the line level input.

If my other advice does not work. Another option is to buy a XLR to female TRS converter (or make your own smile ) and use the mic input on the 11 rack (http://www.amazon.com/TRS-Female-XLR-Male-Adapter/dp/B0024X7XL0).

This is probably the best option as it will allow better control over the signal (pad/gain).
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I'm a practicing guitarist, one day I hope to get it right..