Talk about having to jump through hoops
Worked out 'Group By' sorts on the value of the tag
after any processing by virtual tag
'Sub Grouping' sorts on the value
before
@johnmillsjr
Because you don't use Album Artist, had to do some major re-thinking on this!
You will need to create a virtual tag (NAA [No Album Artist] maybe?) with the formula
You can go back to just sorting by Album
Set your 'Group By' to the new virtual tag
Set 'Sub Grouping' to VirtualGrouping
If this doesn't work then I'm out of ideas