Dave,
Got it working, by uninstalling Soundflower and installing JACK (the download is at
www.jackosx.com . Officially it's a pre-release (current version is 0.74), but it configured first thing running. There are a few setup steps involved, but the documentation is excellent by any standards, and astonishing for open source. (BTW, I'm using Presonus Firebox as my interfrace, and aggregation didn't seem to be required.) Once I added enough inputs in the Studio Bundle to see the Jack inputs, I was ready to go.
That being said, I'm rather disappointed (but not surprised) that all of the software instrument tracks in GB are mono. It looks like NI's Bandstand is going to be next on my buy list.
Thanks again for your willingness to help. Let me know if JACK works for you as well.
-- Mark