Wolfie's suggestion is a good one IF engaging the mute function on the INT-150 to disable its outputs to the speakers does not also disable the pre-outs. I don't know whether or not that is the case, and the manual does not provide an answer. Perhaps someone having specific familiarity with that model will chime in, or else an email or phone call to Pass Labs should provide an answer.
Regards,
-- Al
Regards,
-- Al