A PCIeMadi card in the PC would let you connect the UFX lll via MADI optical cable over long distances, recording room in the other side of the town...
The PCIe bus is often the better way than onboard USB busses, depending on the architecture of the motherboard.
In your case I would connect the ufx to the PCIe USB.

Sorry, but it is nonsense to use a PCIe MADI card for the only sake of connecting an UFX III to another room only a few meters away and operate it there in standalone mode. Makes operation to a pain if everything needs to be routed through MADI and if you have no direct control over the UFX III via TotalMix FX.

It's much easier to use a USB extension that works.

@GussySound: BTW … you didn't tell what extension you are currently using...

I would use this Sonnet USB3 card because the FL1100 chip is proven and has been tested by RME.
https://www.sonnettech.com/product/alle … 4port.html
Then you have this card as a basement and good working reference for connecting directly with USB3 cables up to 3m.
Besides this, two more advantages:
- driver uses the more efficient MSI interrupt handling (message signalled interrupts)
- driver is  included in Win10

In combination with Startech USB extensions which run very well. They are IMHO even better than the corning solutions, which are expensive, but not durable (from what I read and based on my own experience). Additionally the corning cable creates nasty loops, a real pain. These "optical cables" do not even provide full galvanic isolation as one might think. They have thin copper cables to transport USB bus power to the other end.

Based on my experience, the StarTech USB3 extensions are better, I have two and they run well with USB3 and USB2 devices (one for UFX III, one for ADI-2 Pro FS R BE).

It is even possible to "stack" a certain number of these extensions, see further information on StarTech webpage:
https://forum.rme-audio.de/viewtopic.ph … 71#p210971

Your Simplecom EC312 USB3 card seems to use an ASMedia ASM1142.
ASMedia controllers (especially the older ones) are known to have issues with USB3 transfer modes.

See manual chapter 40.3 USB Audio
"ASMedia: not compatible. Newer versions and hubs are partly compatible.
Fresco USB 3 chip: fully compatible (among others)."

So it is likely that your problems are based on that ASMedia controller. Newer ones seem to work.
I have cards with ASM2142 and ASM3142 (2017) that also worked. But I made only quick tests of maybe half an hour.

I still prefer cards with FL1100 chip and can recommend them because they are supported according to RME and I made good long-term experience with them.

Sonnet cards with FL1100 controllers have often been recommended in this forum and have helped well in similar cases. Unless there were perhaps other things behind the audio dropouts, which cannot be completely ruled out.

I think in the end the results are more important, and compared to the UFX III itself, the cost is pretty low.

This card costs here in Germany around €58 which is a reasonable price for a card of higher quality. This is around 96 AUD.
https://www.heise.de/preisvergleich/son … 48037.html

A few additional comments from my side:

For the reliable operation of a USB recording interface, you simply have to use a controller in which the USB transfer mode for audio transport is implemented in conformity with the standard / without errors.
If this is not the case, then it may still work for pure data transport because other transfer modes are used and because retransmits are possible.
Audio transmission is like telephoning over a network (VoIP). The transmission simply has to work, as nothing can be repeated with voice or video.

If the controller has a fault, which can happen, then even a driver cannot fix it.

Example: TI XIO2200A. Such problems have also occurred with FireWire, even with the highly praised controller chips from Texas Instruments. The XIO2200A was installed on many cards.  The XIO2200A chip used an interrupt handler that was unable to reliably handle the interrupt requests from FireWire devices. This caused the chip to sometimes miss interrupts, resulting in audio dropouts and other audio issues. The issue was particularly pronounced in systems with high CPU utilization.

So, it is better to invest in quality at this point, if the basis (error-free transmission) is not guaranteed, then issues are inevitable.

Also important: quality cables with good plugs

See also manual chapter 40.3 USB Audio.
To identify issues in that matter, you can activate CRC checks in the driver by keeping the driver setting window open.
If the CRC counters stay at zero, then you have no issue.

Good USB3 cables you can get from Lindy at a fair price according to the quality. They have 3 shields. Up to 3m is allowed according to the standard. I am using these cables without any issues since years:
https://www.lindy.de/3m-USB-3-2-Typ-A-a … ;ci=800504