NAS + Ethernet DAC = lossless transport ?

Better is the question. You will have bit-perfect data from the network device, but as Kijanki says, the jitter from the CD transport may actually be lower, resulting in superior sound. Depends entirely on the master clock implementation in the devices, the Marantz and the Transport.

Jitter is actually more important than being bit-perfect.

Steve N.
Empirical Audio

So, the actual bitstream is better with a NAS. Seems that approximations and interpolations to account for CD imperfections is something that can only hurt the sound quality.

For the jitter, then, why isn't the right product a DAC with a network interface that is internally designed for low clock jitter. The CDP has a read/transport problem to solve, and a jitter problem to solve, two places where it can lose audio quality. The Network DAC would have only one: jitter. The content would arrive losslessly.

Chryos,

Your original question was if network DAC would be FUNDAMENTALLY better. It has chance to be little better but jitter, as Steve said, would be predominant factor. Interpolation might be non-audible if infrequent but jitter converts to noise all the time. Designing low jitter clock involves also low noise environment (inside of cabinet) and that is not easy thing to do. D/A chip and analog electronics has also big effect on the sound.

Network DAC requires computer with bunch of cables that radiates EMI and injects noise to power lines. This noise might not only affect audio electronics but also increase jitter (noise on oscillator's supplies, PCB connections, D/A IC).

I believe that this is the future for sure. The folks at Linn stopped making CD transports some time ago.