Ampeg with jumper cables?

Okay, so I was in the shop today, and I finally got to try out a "classic" setup - a Fender P-bass through an Ampeg amplifier. Yeah, this was the vintage reissue SVT with the silver grille cloth. I tried it out...and I loved it. The P-bass was kind of limited tonally, but yeah, I'd definitely buy the Ampeg first chance. Although I'd prefer something with a black grille cloth.

I wanted to try it out with the normal and bright channels jumpered together, but the guy in the shop wouldn't let me. So to any of you with multi-channel Ampegs (ones with multiple inputs, like before channel switching) or any other amplifier of the sort, does doing this do any damage to the amp? If not, how does it sound?