Interesting thread...
Khoop - wondered if you've considered or tried an alternative to the Blackmagic eGPU? Seems like something like this would work in your Sonnet Echo :
http://www.macvidcards.com/store/p11...Pro_6%2C1.html
Although this solution seems to be aimed at the nMP 2013, can't see why it wouldn't work with the TB3 Mini also?