Ok, the third option on 5897EX does NOT work. I did, however, find the 5859EX Firmware, and was able to use it.
with my Wife's account configured and using XMPP on 5897EX, downgraded to 5859EX, and it converted my wife's account to SIP and then force upgraded back to 5897EX.
Interestingly, deleting all accounts on 5897EX and re-adding my account BREAKS my account.
Had to make a couple of passes via 5859EX.
I believe(!) it now works.