HDSP9632 und Cubase 5 - Einsteigerhilfe gesucht

Well, I did some successful steps by myself. Audio Signal now reaches my Cubase, I am able to record, but…

…one more problem and I spendt many hours yesterday but didn’t find a solution:

The Audio signal is contantly present, it isn’t muted if I change to a midi channel. If I play my B4-Organ via Midi, I hear simultaneously the sound of the keyboard audio signal.

Could this be changed in the settings of the HDSP9632 or a special switch in Cubase?
I am sure it’s a very easy problem, but not for me

Thanks for help
Martin