As far as what it sounds like, go to past recordings George has tracked (which would be where he used lots of GML gear front to back). Earth Wind and Fire That's the Way of the World I think is the quckest way to get "georges' sound" in your head (he'd probably argue with me on this point because he's done better work since then). It used a bunch of proto GML gear and is very unique sounding, very clear and not much heavy tone or distortion in it. For a pop record its still quite unique. All his records have that signature "George Massenburg clarity" thing going on. For different sounds he seems to lean to different EQ curves or different compression rates/schemes, thresholds, rather than different mics, pres or effects. etc. Most engineers use far more dramatic changes/effects for their mixing (and this is not wrong, just not George).
George's work requires in depth listening to grasp I think. I remember when we were visting a young engineer once and George sat at the console demoing a vocal track on a GML 2030 mastering dynamics controller (sounds just like the 8900). The engineer could not hear it and it took a LOT of listens before he did-because the only change was pure dynamic range-no tone differences whatsoever. The enginner had gotten used to identifying compressors by the tone changes and artifacts. George was beside himself for the differences were "so dramatic" to him yet were quite subtle to the engineer. George could NOT understand how the guy could not hear it plain as day.
So the point is, if you understand and hear what GML gear does and appreciate it, there is no equal. But you might miss the whole thing and walk away scratching your head. The GML thing is "get in, get out, leave almost zero evidence you were there."
Brad