Sorry for the delay in responding - I have used my mic both directly into the bose and also through the keyboard. Both ways have worked great for me. Keep in mind I don't sing and use the harmonizer so going through the Bose Directly works ok for me. All said, I have never had any sound issues with the Bose setup and have used it with the following keyboards - Korg PA900, PA1x, PA1x Pro, KMA. Yamaha PSR3000, Tyros 3, Tyros 4, and PSR950, Roland E50, E80, and now my Ketron SD7. None of these keyboards causes any issues with humming or other problems with the Bose Compact.

Deane