Premium Sound available?

[cfcjr]

I have a 2007 MGM ls with 12000 miles I am driving to Florida in, from Mass. This will be it's longest trip since I purchased it. I am looking forward to the trip, however, I would like to be able to upgrade the sound without ditching the original radio. I have the radio with BOTH the cassette and cd. (I like the redundtant radio controls on the steering wheel) Was there an amplifier available (like the Lincoln) that I could add on for a little better sound? I know I could go aftermarket, but would prefer to stay with what was available if possible.

[86VickyLX]

There isn't an amplifier in the trunk? I'm pretty sure there's an amplifier in the trunk. It also houses the wiring for the rear windshield antenna. If I'm not confusing that with something else...