The MQA Decoder works great over USB. I’ve tested with Linux and macOS. All of the various Format colors to indicate MQA formats work as advertised. I’m sure Windows works as well with the proper driver installed.
When using the S/PDIF input on the Tone2 Pro, the Format feature of the LED ring (momentarily shows different colors to indicate the input sampling rate) does not seem to work at all. Since that’s the only indication that the DAC is processing MQA, I assume MQA is unsupported over S/PDIF. It would be nice if the Format display feature worked for PCM sampling rates, though. @Gouwa, is this just a limitation of the current design? I wonder if this feature could be added with new firmware…
I also discovered that DoP is not supported on the S/PDIF input, so USB is also required for DSD playback. Some DACs do support DSD64 over S/PDIF, but not the Tone2 Pro.
One last niggle regarding S/PDIF, the user manual seems to suggest that the S/PDIF connection supports both input and output. In my testing, this does not seem to be the case. Only input is possible.