Ok, I finally got my XM direct working with my G4 mic input. I had two problems the first was a ground loop and the other was a level mismatch. I used a pair of 12db line level attenuators and a ground loop isolator to get everything sounding decent. You might do a little better with more than 12db, but that was all I had lying around and it doesn't appear to cause any clipping on the mic input anymore. You may not need the ground loop isolator, but if you get noise with the engine running that will probably do the trick.