The pre out on most integrated amps allows you to send a signal to a different amp than the one built into the integrated amp. This allows some folks to upgrade the quality of their amp but retain the preamp portion of the integrated. However this is not often the same as having a second output to drive a second amp with the first amp still ingaged. Integrateds differ so it would be best if you ID'd your integrated so someone with specific knowledge of it could comment, or you could review your manual. If you don't have one you might find one on the manufacturer's web site.
