Yeah, I had meant to update the OP. So I've tried with both the Mophie cable, and an Anker one. It worked suddenly one time with the Mophie cable, but haven't gotten it to work since. Pass through works as it should. If I connect it to a PC it detects the phone just fine and have full functionality. USB Debugging doesn't seem to make a difference, and the default connection mode is MTP.
I had gotten one originally, but took it back because I thought it was just a flaw with the product, and did not further troubleshoot. But indications seem to be that it should work with no issues because of the pass through function. So this is the second Mophie I've had.
The receiver I'm using is a Kenwood DDX9702S, I actually have 2 of these units and both exhibit the issue. I have been unable to find any setting on the head unit that might be causing it... Any help is appreciated.