MarkBass Line Out problem

[BullHorn]

I've used my MarkBass' (Combo Head with the 2x10 speakers) Line Out several times when recording and then haven't used it for about half a year.

Today I connected the Line Out to my Lexicon Alpha USB soundcard's Line In, like I did numerous times before and when I try to play/record anything, it sounds heavily distorted. Is this thing borked or am I doing something wrong? I need help, it's too expensive to break.

[BullHorn]

Further investigation makes it weird.

When playing bass->soundcard without the MarkBass in the loop = sounds fine
When recording bass-> soundcard without the MarkBass in the loop = sounds fine
Now the surprising result is this:
When recording bass->MarkBass->soundcard = SOUNDS FINE

The problem is with monitoring with the MarkBass in the loop. It makes no sense though.... The monitor is representing what should've been recorded but it doesn't.