I am running them off a Keces HA-171 amp and DA-131 DAC, which are very "solid state" sounding in the sense that they are very neutral. 5/1/1 setup making the USB-c kinda useless with 1 amp. Havent tried with S4B but I would expect it to do as with Teams. And not as expensive! bought some. Namely at 3kHz but a couple more above that with practically dead spots in between. No hard reset or soft reset attempts will work. I received 2 left foot sandals. So after all that, they didnt fit. Unfortunately the electrican got to this, opened the box, installed before I could check it out.