Well it's been coming up to 24 hours with no phone but I seem to have found my way.
The problem seems to have been a mismatch between BL, CSC and PIT. In trying to get off the Hong Kong set up I wound up with a ZHU BL, BTU CSC and XSA CP and AP. It worked but I had no wifi. tried a few things to get it working and in trying to flash an XSA CSC (I think it was XSA) I got the Knox bit change. With no wifi I thought maybe the problem was the BUT-based CP needed changing. In trying to fix that, somehow I triggered Knox
I tried DL & Install of Omega 6 (it's a 4.3 - not ready to go KK yet) but although it completed nicely (so many ROM's got hidden or system errors in Odin) the phone didn't start. I tried installing Philz so I could run things from the extSDcard but an XSA wouldn't work nor would anything I had below MJ7. Last Phone Info view I had I still had a ZHU CP, even though AP and CSC were XSA-based.
Finally I got the MJ7 ROM from http://forum.xda-developers.com/show...e-odex-bl-free
and it did the trick.
It's been a learning experience but I'd be happier if I knew for sure both what triggered the Knox bit (I was being very careful about it) and why some of the other ROM installs simply didn't work.