ACI doesn't sell these any more as their distributor stopped making them. This is a very transparent solution to removing the lower frequencies from an audio signal. goes in bewteen pre-amp and power amp. Typically you then use a second set of outputs on the pre-amp to send the signal to a subwoofer with a low pass filter.
This little unit did not harm sound quality at all to my ears. Hi pass frequency is 65 Hz. It has a nice steep 12 db/octave slope.
Sold new for $185, and is less than a year old. Unit is in excellent condition, with very light use.
Thanks for looking.