I added a mono sub amp and a four channel main amp to my van. I tried Metra LOC's, to no avail. Then I tried Kicker LOC's, also a fail (they would actually send a high-level signal to the amps). Then I tried direct to the amps high inputs, also to no avail. Put this little box in place, switched the switches appropriately, and it sounds amazing! :) Less expensive than the bigger brands, but does the trick. No "bass restoration" which is fine, since you can't "put back" what you don't know what's missing. To me that's all mumbojumbo to begin with.