It seems to be risers that were making things difficult. I was about to order some new ones and then I remembered someone saying they just switched them around and got them working. Here's what I did:

1. clean install of windows in UFEI bios mode with all 6-cards plugged in
2. updated windows and all components including gpu drivers
3. paused windows update
4. used amd cleanup utility
5. used DD clean in safe mode
6. installed blockchain driver one card at a time in 16xpcie slot (two restarts per card)
   a. if a card did not behave, this is where I tried another pcie riser until the card worked.
   b. i then used what i thought was a faulty riser board with another card and all worked just fine (can't make heads or tails of this, but it is what it is)
7. I then plugged in each card, let it install and rebooted a couple of times.
   a. this worked up to five cards. when installing the 6th and final card i get the BSOD.

It was stable running Cast-xmr and xmr-cpu, both overclocked and undervolted overnight. I shut it down this morning to work on card six.