Allen & Heath Zedi 10FX

Bought the mixer in the title when it first came out, tried to use it as my audio interface at the time and had no luck.

I decided to re-visit it and get crackling audio playback whatever I try. So far I’ve tried:

5 different PCs, all recent and well spec’ed all drivers up to date.
4 different OSs, Win 7, Win 8, Win 8.1, Win 10 all 64bit all with latest updates and audio optimised.
3 different Zedi 10FX driver revisions.
3 different VST hosts Cantabile 3 Performer, Cakewalk, Vienna Ensemble Pro 6 all up to date versions.
About a dozen different VSTi plugins.
A gazillion different USB cables in every available USB port.
16 bit and 24 bit at 44.1, 48, 88.2 and 96 KHz.

All my other interfaces work perfectly on all my systems.

Has anyone got this to work? Do I need to know a special secret handshake? Do I need to offer “special services” to someone at Allen & Heath?

I want to downsize my live setup and this mixer is fine to replace my X32, it would be nice to not have to use a separate interface.