W4S finally got back to me with this response:
" So a 1k load is quite ridiculous really, not sure why they would release something like that but surely don’t drive that single-ended. Running balanced will drive it and whatever degradation would be common to both phases so likely to cancel out. I can test a DAC to see how it handles it if you wish but I suspect it would be fine".
I’m afraid all this technical lingo is above me, could I please trouble you to comment on this response? Is the fact they "suspect it would be fine" acceptable in your mind?
First, to be sure it’s clear, you would not be driving 1K with a single-ended connection, as the input impedance of the single-ended inputs of your amp is 50K.
Regarding ...
Running balanced will drive it and whatever degradation would be common to both phases so likely to cancel out.
... My understanding is that balanced operation tends to cancel even order distortion components (e.g., 2nd, 4th, 6th harmonics, etc.), but not odd order distortion components (e.g., 3rd, 5th, 7th harmonics, etc.). And generally speaking odd order distortion components are more objectionable than even order harmonic distortion components.
However, given that he "suspects it would be fine," and given that you are happy (or at least encouraged) with the results you are getting at this point, I suppose it is reasonable to put this issue aside.
Regards,
-- Al