I don't know much about the technical aspects of it all, but I know the ART does make it sound better. Yeh, it adds warmth, but it also adds depth, which may or may not be the same thing. My pre-amp also has the phantom power which is needed for alot of mics, and it has a meter so you know where you are before you even hit record. For instance, if I just plug the sm58 into my soundcard, it sounds kinda thin. As for the noise issue, I have noticed less noise since I started using the pre-amp. I use XLR cables from the mic to the pre-amp, then XLR out the pre-amp to a 1/4 plug with a stupid 1/8 addapter into my soundcard. I use the line in port also, if I use the mic input it just doesn't work worth a crap, it may have something to do with the power boost built into the mic input. Without the pre-amp, I have to use the mic input for the power boost, but the pre-amp has it's own power boost, so that solves that problem. The ART does have plugs for 1/4 inch if you don't have any XLR cables, but I have been told the XLR is a better connection, and eliminates some noise. There are input and output knobs on it, so I can adjust things from it rather than mess with the soundcard controls. I have my soundcard control about 3/4 cranked, then I just control my levels with the output knob on my pre-amp. It did take some messing with to get just the right mix of input and output to make things sound best. Too much input does add noise I found. Like anything, you just need to find a sweetspot and go from there.
Curtis
Oh, and I have used the vintage warmer plugin, and it just doesn't sound as good....