Video Hub for external monitor - What model works?

Your iMac Pro (2017) has four Thunderbolt 3 ports.

You can connect two monitors or adapters, with resolutions up to 4K @ 60 Hz each, to one of those ports by using a Thunderbolt dock or hub.

• The device connected directly to the Mac has to be a genuine Thunderbolt device, and the cable connecting the two has to be a Thunderbolt cable. This provides a data highway that is wide enough that the Mac will be willing to drive two 4K monitors or one 5K monitor over it. (On your Mac, using 5K displays reduces the total number of displays you can have; but with your proposed configuration, that is not an issue.)
• The Mac has to have enough free display outputs (yours does).
• Given that, there are many Thunderbolt 3/4 docks and hubs that can drive two non-Thunderbolt monitors. Some bring out a signal on a HDMI port or DisplayPort, and have you use their Thunderbolt daisy-chaining port to hook up a USB-C (DisplayPort) display or adapter. Others split the Thunderbolt chain into several, and let you hook up two USB-C (DisplayPort) displays or adapters.

I would suggest looking at offerings from the following three vendors (all of whom I believe have a lengthy history of offering Thunderbolt products to the Mac community).

• Other World Computing (MacSales)
• SonnetTech
• CalDigit

SonnetTech has a Thunderbolt Dual DisplayPort adapter (not to be confused with a similar DisplayLink one – which you don't' want), and OWC has a basic Thunderbolt hub that splits one Thunderbolt port into three plus a USB-A port. But there are also any number of more elaborate docks from these vendors, depending on your needs.

I see in your diagram that you say that you have an OWC Thunderbolt Hub attached to your third Thunderbolt port, but that this device "cannot handle more than one 4K HD display."

I don't think that's accurate. According to OWC's description, it can handle two 4K displays. That's one of the big advantages they show it as having over a plain USB-C hub!

https://eshop.macsales.com/shop/owc-thunderbolt-hub

Currently you have it set up as follows:

• Downstream TB port 1: Rode microphone
• Downstream TB port 2: 1080p external display
• Downstream TB port 3: Logitech HD camera 2
• USB-A: empty

If you wanted to use it to drive two 4K displays, the configuration would need to be along the lines of

• Downstream TB port 1: First 4K external display
• Downstream TB port 2: Second 4K external display (has to be on its own downstream port, not daisy-chained)
• Downstream TB port 3: (open)
• USB-A: (open)

You'd then need to figure out how to juggle connections for the Rode microphone and the Logitech HD camera 2, but it seems likely that both are USB (not Thunderbolt) devices, and that one could be moved to the USB-A port.

I'm not sure what device is connected third USB-C port, though if it is SSD/HDD drive which has yet another USB-C port, you should get the monitor which is able to connect daisy chained(USB-C daisy Chain connection must be monitor is the last device.).