98 Deville Radio specs

Does anyone know how much power RMS per channel the standard AM-FM stereo radio with cassette has in a 98 Caddy Deville? I put some Blaupunkt speakers in the rear and expected to see a major improvement, but unfortunately I did not. The factory speakers must be pretty decent, a guy at Best Buy said the next step would be to put a Pioneer or Alpine radio in with up to 24 watts per channel and that would improve sound. He guessed the factory unit has 4 to 8 watts per channel. I'm sure it would help somewhat, but I am surprised the factory speakers are comparable to the Blaupunkts I put in. The magnet weight on the factory were as heavy as the Blaupunkt for whatever that's worth? I'm not into the massive subwoofers and amps, I just want some decent stereo as I drive in my commute. Any suggestions are helpful, thanks!