I have a Harman Kardon HK3480 receiver connected to a Music Hall turntable, a pair of Polk speakers and a DefTech sub. I originally connected the speakers via the sub using the speaker inputs, but the receiver also has a sub out, so I thought I would try that. The problem is that originally I could adjust the cross-over via the sub, but now I can't set this via the receiver.

How does the receiver establish the cross-over level? Is this adjustable? I noticed that other similar receivers (Denon DRA-395) also have a sub-out. Do they have the same problem?