Can I use integrated as standalone pre and/or amp?

My main system is suffering from a weak left channel, especially noticeable at low volumes. I've ruled out source as the culprit, as the problem exists with both turntable and CD player. I've also checked and double checked to make sure all connections are secure, and even swapped interconnects. With source and interconnects ruled out, that leaves either the amp or preamp.

I don't have another amp or preamp to slot in for the purpose of ruling one or the other out, but I do have a Marantz PM6004 integrated in my secondary system. Can I run my preamplifier into a source input on the integrated, thereby using it as an amplifier? Or, could I possibly use the integrated as a standalone preamp by connecting my amp to the recorder out jacks? (Sorry if these are silly questions.)

If using the integrated won't work, does anyone have a guess as to what might be causing my weak left channel?

My amp is an Odyssey Khartago Extreme, and my pre is a Decware CSP2+.

Thanks for your help.