i just wondering, my HU has a blue sub RCA cable and two sets of other RCAs that all can go to the amp. Right now i have the blue sub cable going to my amp and i think it sounds good hits pretty hard, but i can't use the controls on the amp. so i guess my long winded question is let the HU control things or let the amp. Thanks I.T.
You can use the controls on the amp still. In fact, you probably are, but it might not be as noticeable is all.
I personally prefer using the filters etc. on the head unit because they can be adjusted more conveniently, and the difference in quality of filtering is negligible.