So I drive a '95 Mercedes (long story), and the radio just went out or has a bad connection. But it will cost me much more than $100 to have someone pull the dash to look for the problem.
You've got a pretty good start on what I want with the SP850 3in1 speaker/radio for the car or anywhere. I'd like to see the same kind of device that sends its output to 2 or 4 decent quality speakers that can be attached to the doors, behind the rear seats, or to the dash.
Given your prices for your current products, I'd think you could do this for $75 - $200. I can see that high-quality speakers is not really your forte, but you could pair with a speaker manufacturer for this product. It would be a lot easier for an old guy like me than having Best Buy or some guy tear into my dash and run wiring all through the car.
Or maybe a suitable product already exists . . . .