Question about Club 3D Thunderbolt 3 on Dual HDMI 2.0

Yes, HDMI supports video + multi-channel audio simultaneously.
The adapter supports HDMI2.0, which in turn should allow 32 audio channels.
I haven't tested it because I use it with 4K PC screens without audio.

DolbyD, DTS and degleichen up to 7.1 have been supported without problems for several years with previous HDMI and Thunderbolt versions before HDMI2. Since HDMI is basically backwards compatible, this should probably already fit.

It seems to me that the question of what the source (medium, SW + HW) exactly supports (e.g. Thunderbolt3 not USB-C etc.) is more relevant.