We carry a wide selection of car audio amplifiers at Hifisoundconnection.  If you need to add some serious power to your audio system's speakers, subwoofers, or both you're going to need an amp that fits the job!  If you are unhappy with the current sound quality, and output of your current speaker set-up try adding a 4-channel amplifier, you will be amazed at the difference in overall sound quality and output.  Want to add some serious bass to your system?  Well you sure can't power a subwoofer off of your head-unit, you'll blow it!  What you need is a high powered mono / class d amplifier to give your subs all the power they need.