Rob Wilkesin, Pipe..
Thats exactly it, its the fact that with a TS you are cutting the lows before they clip in the amp sim, so, you get what some call tight distortion. The inverse of that is a BIG MUFF sound. Big muff adds the lows..
If anyone wants to experiment with this, use our Treble Master and adjust the input frequency to all lows, then adjust it to all highs, you'll see exactly what we're talking about..
Here's the Treble Master..
http://dl.dropbox.com/u/923791/TrebleMaster.rar