almost there. Very dumb question (you are used it to by now) does the high pass filter go between amp and main speakers? Or between preamp and amp?
OOPS for the 3rd time. I didn’t see this. Not a dumb question.
The high pass filter goes in between the preamp and the amp, the connections would be RCA cables. The high pass filter would have RCA outs to go to the subs.
What the highpass filter would do is only allow 80 hZ and up (if that was what it was set at) to go out to your amp. Therefore your mains would only see 80 hZ and up. However, the high pass filter would be sending the full frequency signal to your sub, where your existing low pass filter (which seems only adjustable down to 80 hZ) would regulate where the sub is supposed to start making bass.
However, I have been told, that even with these filters in place, the frequency cross over point is not usually a clean chop off, hence you might still need to play around with the low pass on the subs (from 80 on up).