JackD, the unity gain on the DAC-10 is 93 for the low gain setting where you get 2V in and 2V out. At the high gain setting, at 93 vol you have 2V in and 4V out.
The fact that with the DAC-9 you don't get switchable gain, it always stays at this 'high' value. While I agree that 94 is the value where the signal is not affected by the attenuation or volume control, there is still a 6dB (double voltage) gain. At full 2V in, that would yield 4V out.
There are a number of devices that have a max input of 2V. So, for those, and having a fixed gain setting, we would need to know the volume value that, while attenuating and possibly degrading ever so lightly the signal, achieve a 2V output.
And it doesn't matter at all what equipment I have to know you could be wrong, but I have DAC-10, ST-10 and uDSD. Never have seen an Ida-8. Not sure how that was relevant, though.