OK, I have some (but not a lot of) time to devote to MAD again. :-)
Re: 24-bit vs. 32-bit output
There should not be any difference in quality; they are identical except for the least significant byte of 32-bit output which is always zero. The only reason to have 32-bit output is that some hardware will have an easier time with 32-bit words since it is an "even" number (4 bytes instead of 3.)
Re: oscilliscope and VU meter, et al.
Pierre is right, it's a problem with Winamp that these visuals don't grok 24- or 32-bit output. I *could* work around this by feeding a lower resolution to the visuals, but it would cost additional CPU. Like kaiwei, my preference would be for Nullsoft to fix the problem at their end.
Re: high quality audio setup
Nice work... kind of ironic I don't currently benefit from 24-bit output myself. Maybe Santa will replace my SB16 this year. ;-)
Cheers, -rob