When it comes to controlling volume in WinXP, or any OS for that matter, your introducing distortion into the audio stream anytime your not at 100% max volume...
Dithering can help, if available. Using AudioMulch myself, gives me the option to dither the output. But it's still a band-aid.
I like the idea of having an in-line, pre-amp ANALOG volume device...and I think I might implement something in my car in the future along this idea.
And I'm guessing the CL-RLC basically does what Windows does....digitally alter the signal.
You could even go POST-amp, with something like this...
Just gut the hardware and knob and mount it in-dash?