The digital chain is going to be unbroken right through the system. There is no discrete DAC*. There is a 16 core XMOS processor that does all the USB, S/PDIF and DSP, including sample rate conversion duties, EQ and volume control. The webpage is a bit odd, it implies DSD is directly converted to audio, but this is a trifle difficult. The AX5689 only sucks on PCM over I2S. It is hard to imagine that the DSD conversion is not performed in the XMOS processor. The ADC, one assumes, feeds into the XMOS processor as well.
The overall configuration of both the SA400 and VMW A2 are a bit odd. The SA400 does not present any digital inputs, and uses (we assume) a couple of the spare ADC*s on the AX5689 to provide analog input, and they add specialised analog tone and volume control chips.
The VMW2 could easily have forgone the analog input altogether and satisfied 99% of users. The only sensible use case is for intrinsically analog sources - so tape or phono. The obvious configuration is a digital only device, one that basically packages up the digital inputs of the AX5689 in a useful manner. Somehow it seems that their marketing advice is that they need to produce products that are just a tiny bit weird. The additional BOM for the analog inputs here probably adds $50 to the RRP. Personally I can't see ever needing or wanting them.
The performance differences between the SA400 and the VMW A2 remains a puzzle. All indications are that the power amp is identical. In both cases it seems the analog inputs have been messed up. Given that is all the SA400 has, it seems quite a shame, and makes the SA400 a product without a reason. There could and should be a middle ground product, similar price to the SA400, digital inputs only.
*The subwoofer output is another matter. This could be obtained in a whole range of ways. There could be a DAC and the XMOS processor creates the filtered signal, all the way through to a bit of analog filtering sucking directly on the speaker outputs. I fear it is the latter. Clearly we are on the cusp of the near perfect building block, but somehow nobody is prepared to make the last step. The plate amps from Hypex with internal DSP are achingly close as well, but not available as a turnkey consumer product.
*ETA, I originally wrote DAC, which is clearly wrong, the AX5689 doesn't contain any discrete DACs, but does have spare ADCs.