You may be better off connecting the Depths speaker level input to your amp. This always worked best for me with 2 channel. If you are using LFE out from an AV pre, I just used a Monster M1000 series sub cable. Both are actually for sale.
subwoofer cables
Looking for recommendations on single ended cables (1.5M) to connect a Mark Levinson 380s pre amp to a Martin Logan Depth subwoofer. The balanced connections on the pre amp are running a pair of Levinson 436 mono blocks, which are hooked up to a pair for Revel Salons I just got.