I've been working with the Apricorn folks since early in the year. They duplicated the problem and came up with a firmware fix, that solved the issue. Both the Solo x1 and x2 coexisted, but being the fool that I am, I got a second Duo bought another SSD, this time a 512GB 840 Pro and I'm now running 4 SSDs (1 original Series 840, 2 840 EVOs and the 840 Pro) along with my 3 Internal HDDs and a 3.5" Seagate internal SSHD. And, of course, 2 optical drives. Wow, 10 drives inside my Tower. Try that in a nMP.
I gave both my external drives the boot. Packed 'em away for a rainy day.
The Apricorn folks were GREAT to WORK with, and I thank them for their efforts in helping me solve my problem.