HD Native Thunderbolt and HD Native PCIe on Same System?

[jb_trm]

Pro Tools HD 2018.1 here on a 2013 Mac Pro running macOS 10.12.6.

I am switching my configuration over to a HD Native Thunderbolt and a Focusrite Red 4Pre. Both Port 1 and Port 2 on the 4Pre and the HD Native Thunderbolt are connected. This uses up the 64-channels on the HD Native Thunderbolt, of course.

Question: Can I add an HD Native PCIe in a Thunderbolt expansion chassis and add another max 64 I/O channels for a combined max 128 channels?

Note: I intend to put a couple of Focusrite RedNet 5 on the HD Native PCIe, if the above configuration works.

Any input is appreciated!