Adding the right external amplifier to your car audio solution not only results in higher volume levels, but also fuller, cleaner sound at moderate volume levels as a strong amplifier can operate more efficiently than the receiver alone. But adding an amp creates the small problem of find a place to mount it and then wiring it. Alpine has a solution for owners of its car audio receivers (2005 or newer), the KTP-445 Head Unit Power Pack. I had an opportunity to check the KTP-445 out at CES 2009.
The KTP-445 is a small-form-factor (6 inches by 2 inches by 1.125 inches) power upgrade that installs inline between your Alpine receiver and your vehicle's wiring harness. Depending on the vehicle, the device installs in minutes and can fit in the dash, behind the receiver. No special wiring is required.
For your trouble, the four-channel amplifier boosts power to the speakers to 45Wx4 RMS (up from an average power of 18Wx4 RMS). According to Alpine, the KTP-445 uses an advanced digital design that provides an extremely clean power output with very high efficiency, making the bass tighter and highs clearer. According to my ears, the KTP-445 produces fantastic sound for a $140 device the size of a small burrito.
I believe that the KTP-445 is boosting speaker level outputs instead of the cleaner preamp outputs that most receivers use for supplying audio to amps, so an external amp may still be the best option for audiophile sound quality. But for the rest of us who can't tell the difference between 256Kbps and 320Kbps MP3s, the KTP-445 offers a good sounding, easy to install alternative for your Alpine head unit. Just make sure you upgrade your speakers next, because stock paper cones probably won't last too long under 45 watts of continuous power.
We should be getting a KTP-445 for testing around April 2009.