I've been using the Great River preamps for a few weeks now and I'm loving them. Aside from their sweet microphone amplifying characteristics they're also great for running mix stems through.
I've been experimenting with running the stereo mix of my drums, bass, guitars, keys through the Great Rivers and I have to say I love the final result. The mixes I've been doing have been more musical and sound, for lack of a better explanation, more expensive.
I'll put some sound clips up soon of before and afters but here's a picture of my digital mix stem of the drums and then what it looks like after it runs through the Great Rivers. Compressed much? :)