Hi Ken,
I can't recall if the EP350 v3 has separate high-level (speaker-level) inputs (it must have to enable operation with older gear lacking a dedicated subwoofer output). If so, you could use those to check if the sub is actually working or not. Just connect one of the left or right speaker leads to the high-level input and see if the sub activates with music programming.

Regards,
Alan

Alan Lofft,
Axiom Resident Expert (Retired)