I had the same problem while using the default recorder from my SB live 5.1.

I deceided to use Cool edit to record. It did solved the problem. I record in wave at 128 bps stereo and then convert it to mp3 mono.

I do have a zoom too. I go out from the line out into the microphone jack using an adapter. The important thing is to be very careful while using the mic so that the sound is not too high, it may damage your card. On the propreties of the mic volume, I could take out the +20 db setting.