Ok. I don't want to argue with you about cables. It's really pointless.
That being said, if there's a difference between the Perfectwave and Directstream, I have no idea what could be causing it. I assume they both have the same transport mechanism, and I can't imagine that they do any sound processing, but who knows? Perhaps the decoder in each product is making a difference, and if you say there's a difference, then there's a difference.
Either way, it's not likely that one is getting different *data* than the other. It's how it's processed and sent to the DAC. I don't have an aurender to compare to the M50.2, and I don't know the conversion steps (D->A->D?) but the M50.2 claims it does D->D. If you accept that, then there is no extra analogue step required in the decoding due to the use of PWM. Sound quality is really good, but there will always be someone who will tell you they like one over the other. I would say it's subjective, but to me, it's very much good enough.
I received an email from NAD support. They've said that "we are an airplay 2 partner, the details of the integration and compatibility are not yet available. As for DSD, it's come up a number of times, however we cannot comment on the future of any upgrades. The M50.2 does not do multichannel audio."
Two things to pull from this email:
1) Airplay is obviously being considered, but timeline is unknown. Based on their other products (M17) I would assume DSD is not likely to come either. This product is software driven, but there may be technical difficulties in how the data is piped to outputs.
2) I was wrong about MCH. I don't know why I thought I read it supported multichannel. Not super happy about that, but to be honest, I don't have any multichannel audio anyways. That being said, if you want that feature, I would consider the Nimitra Fidelizer. The Aurender is also stereo only.