I don't have anything more sensitive to test with, maybe Ddoingwell has something? For practical use for me it's a non-issue, but it could be an issue for others.
Regarding the hiss, you may find that it's your source that's giving you that. If possible, try a few different sources, even try running the amp directly from the output on a CD player or off the record/pre-amp outs on an integrated amp. Barring that, try different volumes on the source you do have. I'm not getting any hiss though when the amp was newer, there were a few teeeny weeeeny crunchy bits coming off the volume pot as I turned it up/down that went away after about 12 hours. Also, my first amp developed a flaw and has been returned to the magnanimous Dave who has sent me a replacement before even waiting for the troubled amp to reach him. Seems that the over-heat protect in the chip was a bit trigger happy and the amp would shut itself off after about an hour of use. It would come back after a while but it was a pain so Dave offered to replace it immediately. Sound-wise, it's still magnificent and when the new one arrives, I'll comment more fully on the sound. I have a Meier and a PA2V2 as well as a Classic 10.0 pre-amp with headphone amp in the output stage for comparison.