I guess by "robust", I mean rich, lush, and/or powerful...not just in low-end response, but across the whole spectrum. In all my listening to Aerco recordings, I always came away with the feeling that they were really detailed, and that they added so much depth to recordings. While maybe not totally transparent, I think what I just described would complement almost any microphone.
There's an Aerco over in the yard sale right now, BTW.
Best of luck "searching for the sound".
I used to have a Phil Lesh shirt that said that on the back!