I've got a few lower impedance headphones and iems and it works hiss free for all of them (AD1000PRM, DT770 Pro Limited, Monster Gratitude). Granted, you might only have about 5 steps of the volume control to play with on the iems and 10 on the headphones, but it's nothing that can't be fixed with an impedance adapter.
I listen to my balanced LCD-3 and HD 800 in the 8-10 range on low gain and HE-6 in 15-20 range on high gain. Keep in mind that each gain setting has 99 steps.
Was the noise floor audible with those cans? If so, looks like a real winner at that price no doubt!