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.
Never doubt there is Truth, just doubt that you have it!