RE: Audio cuts out intermittently with factory Sirius satelite radio installed...
If that's the case and you can get it for that price and do the install, it's not such a bad deal. I've had Kicker subs and speakers before and the've been great. It all depends on your needs. If you listen to a lot of rap or hard rock and want loud, hard hitting bass, or you are looking for a really loud system, I don't think you're going to be satisfied. For that you will need at least 300 watts RMS powering a single or pair of 10" or larger subs. The type of box makes a difference too.
Sealed box = best for a "tight" bass sound that is very accurate but with not very much boom and thump.
Ported box = best for a wide range of styles of music and falls somewhere in between sealed boxes and bandpass boxes.
Bandpass box = very loud, boomy and efficient; great for rap, disco, and hip hip but not the most accurate musically.
My personal choice for speaker brands are Polk and Pioneer if you want the best bang for the buck, and Alpine orBoston Acoustics if you want to spend some cash. As for the setup, I prefer components in the front with 6x9s for rear fill, with a 4 channel amp (or 2 two-channel amps), so each set of speakers are amplified. For the sub, I use an Infinity 200 Watt Bass-Link, which sounds very good, but I keep it in the back seat most of the time since it sounds louder and better than keeping it in the trunk. I also have a bandpass box with a 600 watt amp running 2 12" Kicker competition subs that I can swap in there. The car is slammin' with those in the trunk!
Bottom line is you have a lot more options going aftermarket but it all depends on your needs and your budget. Don't forget, when going aftermarket you don't have to buy everything all at once. I got my H/U first, then did the rear speakers, then the fronts, then got a wiring kit and sub, then got the amp. Also, as I said in my post above, my Kenwood H/U handles home burned CDs much better than the stock radio did and I can play CD-RWs and MP3 and WMA files.
Good luck, hope this helps!