So I'm guessing that now it sounds even BETTER than before.
Why do you need ASIOcaps? What program does not like accepting 24bit?
Using 16bit will also be lowering the sound quality, but if thats what it takes to get working then so be it. 16bit also has a lower dynamic range than 24bit. This basically acts like a compressor - which can be advantageous in a car situation, because it helps bring the slightly quieter sounds out a little louder, away from the road noise.