I've had this unit for just about two weeks, and I can report there is absolutely no noise from the unit physically, or through my headphones or speakers. Not sure if this dealer had it confused for a different product, but I haven't heard any reports of humming or power supply noise at all.
According to Amir's measurements at 99 volume you get 5.3 volts output, which is perfectly fine to feed into the SH-9. Absolute best SINAD is just below that which gives you 4.7 volts out, and 121.6 SINAD. There is only 1db SINAD difference here 120db vs 121db between 94 or 99 volume, so honestly either way I doubt the difference is audible.
If you need 4.0 volts out exactly for some reason, which is a bit of a standard for XLR output, you can lower the volume to 94 to achieve that. This could come in handy if you're feeding a different amplifier, or other pro audio gear that is designed for 4.0 volts over XLR.
I use my SU-9 at fixed 99 volume with my SH-9 as that's easiest, and it sounds wonderful. On low gain, I seem to end up between 20-30 volume on the SH-9 most of the time with Hifiman Ananda, and Focal elex, and maybe 34-40 volume with Dan Clark Audio Ether CX. Hope that helps.