Actually, it is a 25 watt RMS per channel amp.

Oh, sorry, I misread your post and thought you were talking 25 watts total. A 4-channel amp, 100 total watts, that's enough to do a decent job of driving your stock speakers.

Then when you build your new car system, you can bridge the Rockford Fosgate amp and use it for a pair of subwoofers and run 50 watts/channel stereo or 100 watts mono, or you could even wire the speakers up 2-ohm (either use 2-ohm speakers or wire 4-ohm speakers in parallel) and force the amp to deliver 100 watts per channel stereo. Whether the amplifier would stand up to this abuse is unknown -- I'm guessing it probably would be OK. R/F amps are popular among the SPL crowd (not the Sound Quality crowd, however) and have a reputation for understating their actual power capabilities.

With that amp running the subwoofers, then you would need a second amplifier for the mids and highs (everything that isn't a subwoofer) and I would recommend something in the range of 200-400 watts total. More wattage isn't just about making more noise. More power means faster transients, and allows you to operate your speakers optimally in terms of excursion and responsiveness. As long as your gain controls (on both the amplifier and the head unit) are not so high as to induce clipping (clipping is sending a square wave AC signal to your speakers instead of a nice smooth sine wave) a more powerful amplifier will not damage your speakers, it will just make them sound better.

I don't have any experience with Rockford Fosgate... any other suggestions?

Not really... what little expertise I have in car audio tends to be in the area of tuning and tweaking existing systems, and maybe a few ideas about basic system design. I kind of know how to listen and identify problem areas, and have some idea of what to do to fix them. As far as recommending Brand X over Brand Y, I am at the mercy of my stereo dealer's prejudices. (For what it is worth, I have a great deal of respect for his opinions!) If it is of any usefulness to you, he is currently favoring XTant amplifiers and subwoofers for sound quality, and MB-Quart speakers for mids and highs. (He says I won't like the MB-Quart subwoofers; they are too dark and atonal sounding for my tastes)

I guess if I had to give one paragraph worth of advice for building a car stereo it would be: Don't rush, think things through and don't do anything until you have thought of several different ways to do it, then pick the best way. Buy high quality components -- the extra $100 you spend now may pinch a bit, but a year from now you'll never miss it and you'll be glad you had the forethought to do it right the first time. Most important of all: You must have at least one subwoofer, my favorite being 10" because of the warmth and tonality it can add to the middle registers.

tanstaafl.

"There Ain't No Such Thing As A Free Lunch"