Hello - I recently acquired a nice Beogram 5000 turntable with a newer MMC3 cartridge. I have connected it to a Bose 321 system using  a 7-pin DIN to  RCA cable (w/ground cable) and plugged it into the AUX port. The Bose system does not have a ground unfortunately. There is sound coming out of the speakers, but the volume is very very low unfortunately. If a different source is selected on the Bose amp/tuner, such as CD or FM the sound is loud and clear. When selecting AUC for Beogram 5000 the sound is low and clear. Does anyone have any thoughts on how to remedy this? Thank you.