Hi Darrell,
to IceInSpace.
I can't bring my DMK to focus at prime focus in my 12" newt - but with a 2x, 3x or higher barlow (I use a 5x powermate mostly), it comes to focus fine.
With a DMK + filterwheel at prime focus, it can't come to focus either. But again with a barlow, it will come to focus fine.
If you're doing lunar or planetary imaging with it, it's rare that you'd want to use the DMK
without a barlow of some sort, so I don't expect you'll have a problem.