Audio Midi setup channel error

I'm trying to setup surround sound output via old thunderbolt device (Intensity Shuttle) which manufacturer lists as supporting 8 channels of sound via embedded HDMI, but the Audio Midi Setup utility returns 16 audio outputs.

I'm unable to configure the speakers in any format other than stereo, neither 5.1 , 5.1.2, 7.1, 7.1.4 etc. As soon as I do and try to apply the changes I get and error message:

Overlapping Channels

Each speaker must be connected to a different channel on your audio device.

Change the routing so that each speaker is connected to a different channel.

Now the HDMI is going to a TV which is using eARC to take sound to a sounder which has satellite speakers (2 rear speakers that also fire upwards, 1 subwoofer) to achieve 9.1.4 surround sound.

Listening to the test sounds per speaker I need to configure it as follows to achieve 5.1.2 surround sound

Unfortunately the device is no longer supported by Black Magic Design.

The audio that comes out currently via the HDMI is not correctly sent to the surround speakers.

If I play a 5.1 sound file (L, R, C, LFE, Ls, Rs) via the Mac or via BM Media Express the tests for each individual speaker come out incorrectly, but if I play the file directly via USB from the TV or Blu-ray player via eARC the surround sound is correct.

Any ideas how else to assign channels from device to speakers/configure speakers?