Back in podcast 269 community member Chase Ryan asked about a suitable PCIe expansion chassis to with one slot to take an HDX card, which needs Aux power and at the time we couldn't find one. 

Shortly afterwards Sonnet announced the eGFX Breakaway Box, a Thunderbolt™ 3-to-PCI Express (PCIe) expansion chassis that also provides the crucial Aux Power with a single slot for connecting any size Thunderbolt-compatible PCIe card, including high-performance graphics (GPU) cards to a Thunderbolt 3-equipped computer with the Avid HDX card in mind.

Community member J.D. Andrew saw our article and ordered a Sonnet eGFX box, for his Pro Tools HDX1 system. All was going well until it came to fit the Aux power lead...

The problem JD had was that the lead Avid supply for the cheese-grater Mac Pro doesn't fit the aux power socket in the Sonnet eGFX. So he contacted Sonnet and JD received this reply from Robert at Sonnet...

The problem is that the AVID HDX card uses a non-standard PCIe board connector and the Apple Mac Pro motherboard uses a non-standard PCIe motherboard connector. Sonnet will make some adapter cables for the Avid Pro Tools|HDX card, but it will take a few weeks. If you can wait, we will send you one. If not, you can make one yourself. 

• Buy a PCIe six-pin extension cable at $2.99 on Amazon.
• Buy a bag of AIRIC 100pcs Nylon T-Tap Wire Splice Connector Red Tap In Quick Splice Self-stripping 22-18 Gauge Electrical Wire Crimp Terminals for 18 Gauge wire @$6.59 on Amazon (Or wire connectors of your choice, but you would typically need a crimping tool.)
• Cut as indicated, strip, and crimp yellow to yellow and black to black.

Robert also provided some helpful images to illustrate his suggestion for modifying the Avid supplied lead to work with the Sonnet eGFX unit.

JD wanted us to share this with the community so anyone considering using the Sonnet eGFX Thunderbolt expansion chassis would be aware of this and could make the necessary arrangements ahead of time.

JD ended his email to us with the line "I hope that I don't have to put the card back in the Mac Pro anytime soon".

That got me thinking, and I remembered that Avid supply two leads with an HDX system.  One for the Mac Pro as shown above in the image that Sonnet sent JD, and a second one for a PC which has the traditional 4 pin computer power connector on it that you see with hard drives and other peripherals like DVD drives. In fact, I still have mine in the box in my cupboard still in its bag...

Unfortunately, this find doesn't fix the whole problem, the power connector on the PC lead still doesn't fit the aux power socket on the Sonnet eGFX but it does mean that as a Mac user, if you still have this PC lead (and unfortunately JD hasn't) then you could use this lead to make the new lead to go from the Sonnet eGFX to Avid HDX and keep your Mac version intact, in case you do need to put your HDX card back in a cheese-grater Mac Pro. Conversely, if you are a Windows PC user, you could modify the Mac lead and keep the PC lead intact.

Hats off to Robert at Sonnet for his detailed support reply and thanks to JD Andrew for sharing this with us so we can share it with you.

Update 8th November 2017 - Sonnet Now Stock The Correct Leads

Robert from Sonnet has been in touch with us to say that they have built some of the proper HDX power cables and now offer them for sale in their web store. They are listed as "Avid Pro Tools|HDX PCIe Card Power Adapter Cable" and cost $39 direct from Sonnet.