I can only report from personal experience. When I record something at 1-bit, it sounds fine. When I dither it to 16-bit or 24-bit at 44.1 or 96 (using the Audiogate software), I don't detect any hiss, buzz or other noises.
If you go to Sonic Studios, he does a series of technical tests on the MR-1:KORG MR-1 Tech Review
You can see with the measurement equipment, he can detect noise going from mic-in or line-in, but the noise is out of audible range.
I have not tested the unit recording to 24-bit or 16-bit, so there may be issues with the A/D converter that the Musician's Friend Reviewer is referring to. Even so, it seems that he is using the unit to record something for scientific experiments, so inaudible noise may be a concern for whatever he is measuring.
Anyway, I think the value of the MR-1 as a playback unit is if you are able to record a source in DSD, then play it back in DSD. For example, vinyl on an audiophile turntable, or from a live recording of a performance (however, I am not sure if there is any additional value in recording a CD to DSD). If used as such, the playback is very stunning, and I doubt you will be dissatisfied with sound quality, despite reports of "noise."
I've been very happy with the unit, except for the battery life.
Originally Posted by Reima
So there should be no problem with DSD playback?