As with most Aux audio devices, the connection to the head unit makes all the difference in sound quality. Your connection will be one of the following, and depending on which you'll have different options, and inherent issues with use.
- Integrated FM Modulator: Most XM/Sirius units have FM modulators integrated into the unit. The upside is if you move the unit alot, there's no wiring to the head unit. The downside is that it produces a very weak, low fidelity signal and is often absorbed/blocked by your vehicle's body and interior, and can often be drowned out by local commercial FM signals, forcing you to change the frequency. A good antenna can improve the signal, but if you're going to spend money to fix the problem, look at the other solutions.
- Antenna-Fed FM Modulator: A device that takes a signal from any stereo line-level source and pipes it into the head unit through the antenna connection by sitting inline between the head unit and antenna lead (think VCR or cable box passthrough to a TV). The upside is the FM station will be very strong and will overpower anything else coming into your head unit. The downside is that being an FM signal, the fidelity is still a little muddy. It also requires a bit more skill to install as it needs a power source in addition to a direct connection to the back of your head unit. I did one in about 45 mins, tapping the 12v lead to the radio for juice.
- Cassette Adapter: The best quality connection achievable (IMHO) to a head unit that has at least a cassette player (I have an '01 ST with the Cass/CD unit), but no direct line input. I use this for my XM and MP3 player and get near-CD quality sound. Super easy to set up and produces fantastic sound.
- Direct Aux Line-in: The best quality signal input available for a non-digital source. Some head units have a connection on the faceplate, some have it on the rear as an RCA stereo input. I even had a unit that had a 3-Source Aux input module made by Sony that I mounted under the passenger seat in my Ranger. Most modern aftermarket head units have this feature, and due to the popularity of MP3 players and Sat radios, some factory units have it as well. This is the Ultimate connection aside from going to a digital interface connection to an iPod, but you said it's a SatRad, and so, most likely has a standard 3.5mm stereo line level connection.
No matter how fancy the sound system is, an AM station will still sound like crap. Garbage In, Garbage Out. Get a good signal from the SatRad to the head unit. If you have a nice setup as you say, hunt down the Aux line-in, tap into it, and enjoy! My XM on line-in was sick!
GL to you.
