I've repeated tests with ArcoLinux (and re-verified in Proxmox): both ASMedia as well as 48:00.0, 48:00.1 and 48:00.3, can be pass-through, and still have proper USB audio with no audio dropout, as long as WiFi is disabled.
I think I'd not initially noticed this phenomenon (if one looks at my original posts on this thread), as I was using the native BT/Wifi card with only the BT enabled. This is becausae WiFi on native AX200 cards has, as yet, no known kexts to activate WiFi on the macOS side. So I had unintentionally inactivated WiFi and good USB Audio with no dropouts.
So possibly, when one is using the TRX40 mobos with a Mac VM, one will need to make one of two choices. That is, based on what you've indicated and what I've found with WiFi, if USB ports and BT are more important and WiFi is not, then pass-through all USB devices but inactivate WiFi and the USB audio/FireWire audio should be okay. On the other hand, if WiFi is necessary, then don't pass-through 48:00.x, and have fewer active USB ports and no BT, but functional WiFi.
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As for PCIe AIC USB cards, I've not posted this to date on this forum, but I've not yet found a card that works on a VM with pass-through, and I've tried many (just as I've not yet gotten a working FireWire card: one more is on order!).
If one Googles on "PCIe AIC USB cards pass-through VM", one can find several threads discussing this issue, particularly starting in 2017. There are references to a few expensive cards, but once one then researches those cards, there are further posts saying that those cards have been modified over the past 3 years of production, and don't always work in a pass-through environment. This is the same situation I faced with FireWire: newer cards are re-designed and now contain a bridge that prevents VM pass-through.
But if you were seeing erratic behavior of your PCIe FireWire card when 48:00.3 is active, then a PCIe USB card will most likely suffer the same fate. This would mean, again reverting to my high-lighted paragraph above, where one must make a choice between USB ports and BT or WiFi for proper audio.