Most factory sound systems can't give you the dramatic and high quality bass range that comes from having a subwoofer. Achieving the bass tone you want depends on power, space, enclosure, sensitivity, impedance, and number of voice coils. You can pair your subwoofer with an amp or purchase a subwoofer with an amp built in so that it's already powered. The bass from your subs will create the sound and feel of a live show happening in your car.
GoldenEar Triton Reference
Kenwood Excelon DVD AV Receiver w/ Navigation Only $799
Pioneer AVH-201BT DVD/CD A/V Receiver w/ Bluetooth ONLY 199.99
Denon AVR-X2400H AV Receiver w/ WIFI & Bluetooth Only $399
Kenwood CD Receiver w/ Bluetooth & USB Only $89.95
Kenwood Excelon CD Receiver w/ Bluetooth & USB Only 129.95
Rockford Power Series T1000-bdCP