Well, I guess tonight I will try to catch everyone... Removing all of the LR would be almost as much of a PITA as trying to catch the fish (it wouldn't even begin to fit into a 20-gal tank), and I have all live sand also.
From what I have read, it looks like hypo doesn't usually kill good bacteria. Among my LR, I have like 50# of rock that started as base rock a few months ago - there should not be too much more than bacteria living on it. I will take out that rock and put it in the QT. In addition to making the angels & trigger more comfortable, hopefully the ~3 months it spent in the display will cause it to bring in some bacterial filtration capability to the QT.
In addition the 20-gallon QT tank I also have an empty 10-gal tank. I am thinking I will use 2 powerheads, one in each tank, with tubing to move water back and forth between the tanks. This way my total volume will be 30 gallons, but I can separate the 2 angels. I'm thinking I'll put Fido the trigger and the flame angel in the 20-gal, and Daisy the CB and the 4 chromis in the 10-gal.
All of this, or course, is dependent on catching all of these fish. It will be easier once I remove 50# of the rock.
I just want to say thanks to everyone for all of the information. I have not had time to read everything in the links, but I did read the article about ich's life cycle - very informative and interesting. One thing I know is that I want to be sure I get completely rid of it, and from now on I will definitely QT (and probably hypo) everyone so it never comes back. At least I am learning my lesson early, before my tank is fully stocked.