Let's get the story straight! ;-)
If you're using the .3mv version of the Dyna then, yes, you should be using the MC inputs. The gain structure is fine, which is why you're having no issues in that regard.
The only question is impedance. This is extremely sensitive when using a stepup transformer and no one can give you more than general guidance. Each system is unique and the adjustment when using an SUT is so touchy that trial and error is the only method for optimizing.
Good luck!
If you're using the .3mv version of the Dyna then, yes, you should be using the MC inputs. The gain structure is fine, which is why you're having no issues in that regard.
The only question is impedance. This is extremely sensitive when using a stepup transformer and no one can give you more than general guidance. Each system is unique and the adjustment when using an SUT is so touchy that trial and error is the only method for optimizing.
Good luck!