If the only device you have in TB3 is an Audio card, I wouldn't worry about it. PCH or CPU won't make a difference.
If you care about PCH vs CPU lanes, then no point getting any Gigabyte X299 board, they are *all* wired via PCH. The TB3 card must be placed in the designated slots:
PCIe x4_2 (https://www.gigabyte.com/au/Motherboard/GC-ALPINE-RIDGE-rev-20#ov)
The Designare is better than the Aorus Gaming 7 Pro (make sure you get the pro, it has the same VRM has the Designare) ; the only exception is that I got TB3 and USB-C hotplug working with the Gaming 7 Pro, but not the Designare....
However, in the future, if you get a TB3 external disk, using PCH lanes will be a worry, especially as the NVMe share the same bandwidth
The Asus X299 Prime Deluxe is the cheapest of those cards, with the most features that's for sure... Your GB TB3 card will work with this motherboard just fine.
I'm very pleased with the ASRock x299 Professional Gaming. It has 10Gbit/s nic (in addition to the intel i211 and i219). There are caveats in getting the AQC107 to work, you *must* go through 10.13.3. There was a bug in 10.13.3 that reflashed the AQC107 into an Apple branded card (the same as the iMac Pro). Once the AQC107 got reflashed, it would then work perfectly in macOS. That bug got corrected in 10.13.4, and the card no longer work. If it has been reflashed in 10.13.3 however, it will work.
In the ASRock, the TB3 card works in any of the slots, without having to configure anything in the BIOS, and all PCIe slots are using CPU lanes.
The main NVMe slot also use 4 dedicated PCU lanes, which will give the best performance.
Another thing of interest over the Gigabytes board, it supports Intel VROC: that is you can split any of the PCI x16 ports into x8/x8, x4/x4/x4/x4, x8/x4/x4 or x4/x4/x8 ... So more storage option (the Asus can do that, but only with their M.2 PCI cards)
The ASRock has massive heatsink and the most over-designed VRM of all.
I have TB3 hotplug working now (not USBC however).
I have all USB ports working, and sleep is almost working (it wake from sleep only after 2-3s, which I'm hoping I will find a solution for).
For now, I've had the best results with macOS on this board.
I wouldn't use the availabity of
@kgp guide as the reason for choosing the Asus Prime Deluxe. You can achieve the same rather easily with all x299 board out there.
The Designare is a great motherboard, certainly the highest quality one I've seen. The only downside is that the TB3 ports go through the PCH.
Using the SSDT-TB3.aml I posted earlier did you manage to get hotplug and usb-c working ?