new sub and amp

Hey guys, I recently bought a jlw3v3-4ohm and an eclipse xa1200 amp. I've been having trouble making decent sound out of them. I think it has something to do with my cd player(alpine cda-105). I tried messing with the HPF and it helped somewhat but if i turn it too low my speakers inside the car sound terrible. If it matters its in a 05 Kia Amanti, What should investigate? Thanks

Can we get some kind of clue as to how it is sounding?

The output is just real quiet, its kind of late so i cant play around with it right now. The cd player goes upto about 35 volume but i can only turn it upto about 15 and that makes the stock infinity speakers go crazy. I turned off the "loud" feature and that actually helped because i could turn the volume slightly higher. I know Im not just expecting more than I should be.