Some additional information for you.
Thunderbolt on PC works well... but you've got to have all the details covered.

• Microsoft added support for "PCIe via Thunderbolt" to Windows 10 (Win7 does not support "PCIe via Thunderbolt").
• Microsoft supports "PCIe via Thunderbolt" in Windows 10... but only for Thunderbolt-3 controllers.

If you have a Thunderbolt-2 controller, it'll work for "Firewire protocol via Thunderbolt", but not for "PCIe via Thunderbolt" (necessary for PCIe level performance).
 
Most Thunderbolt-3 controllers are "add-in-cards".
The motherboard has to specifically have a Thunderbolt-3 header (connects via cable to the Thunderbolt-3 controller)... and the BIOS must support the specific Thunderbolt-3 add-in controller.
IOW, You can't just pop a Thunderbolt-3 PCIe controller card in just any motherboard.
 
Thunderbolt-3 controllers use a USB-C port (here's where it can get confusing).
A USB-C port can carry Thunderbolt or USB-3.1.
Just because a motherboard has a USB-C port/s... that doesn't mean it has Thunderbolt.
Many motherboards have USB-C port/s... that carry USB-3.1 (no Thunderbolt).
The motherboard specifically has to have a Thunderbolt-3 controller.
 
Most Thunderbolt audio interfaces are Thunderbolt-2.
The UA Arrow is an exception.  It's a newer Thunderbolt audio interface... that comes stock with Thunderbolt-3 port.
UA now offers the Thunderbolt-3 interface card for the Apollo-8/16 (~$500).
For the vast majority of Thunderbolt audio interfaces, you'll thus need a Thunderbolt-3 (USB-C port) to Thunderbolt-2 adapter.  Apple makes one for ~$50... and Startech makes one (~$20 more).  I'm not an Apple guy, but the Apple adapter has worked in every scenario we've tried (many different custom desktops and laptops).
 
 
In summary, make sure all these things are in place:

• Up-to-date install of Win10
• Thunderbolt-3 controller
• Audio Interface must have "PCIe via Thunderbolt" drivers available for Windows
• Thunderbolt-3 to Thunderbolt-2 adapter

Can you give the Asus MOBO model number you specify works with the Quantum well? I'm guessing it has the Thunderbolt 3 controller on the MOBO and is working at those PCIe via Thunderbolt speeds.   
 
For me "firewire protocol via Thunderbolt" isn't a huge leap since I'm using firewire now. Thanks for clearing this all up. Any move up would need to be TB3 using that onboard controller.

Thanks for the info Jim.
Asrock H370 Pro4 w/ Asrock Thunderbolt 3 AIC Attached to TB Header on MB (HARD to find..mine came from Japan and took weeks to arrive...) UA Approved Startech TB2 to TB3 adaptor, W10.
 
Upon comparing an Apollo Twin Mkii on my system to the Apollo 8 Firewire Converted with TB2, the Twin Mkii does indeed seem to be running with more stability. Your comments above implied that could be the case.
 
I usually stay away from bleeding edge by using last generation CPUs and MB that are proven. This build I went for 8th gen Intel, new MB and trying to get Thunderbolt on Windows. I do think some consult time with your company would be $ well spent to give a look over this (for me) bleeding edge leap :) 
 
Thanks again for the kind sharing of info.