I have Harman Kardon HK 680 and when I comnect amp pre out to Jamo e7 subwoofer sound is to low. How to connecr subwoofer to HK 680? I tried rca to rca because is mono,1 rca to 1 rca, not Y rca. Pre out amp to Jamo E7.
https://www.fein-hifi.de/images/product_images/original_images/hk680spurg...