What is the sub channel level currently set to in the receiver?
Two choices to start with:
1) Replace the active X-over with Y-adapter and just use bass management of the receiver.
2) Work with the active X-over. It does give you additional gain control.
Set Low-pass to 140
Set Phase to 0
Gain controls will be adjustable as required, in conjunction with the sub level in the receiver. I would start with both at 12 0’clock position.
If you have not already done so, purchase a Radio Shack SPL meter. This will aid tremendously when these type adjustments need to be made.