Well unfortunately then for myself (and a lot of others I imagine) running this DAC power amp direct is simply not an option due to the fixed gain of my power amp and sensitivity of my speakers. I have my current DAC set at 0.5V max output (gain of analogue stage) and I fine tune with digital volume. If I were to run your DAC power amp direct balanced at 6.6V! I would need to use enormous amounts of digital attenuation. I understand your logic for keeping the analogue output stage as simple as possible however for many (the majority?) of people running this DAC power amp direct would simply not be an option.
If this digital volume control were only 24 bits, then I would agree that it would have to chop bits off above the noise floor. OTOH, the TotalDac uses a 69 bit FPGA, so there are are plenty of bits to chop-off without getting into the noise floor even at very low volume. Vincent's design is a true lossless volume control at any level.