Concur: it gets a bit warm whilst playing. I don't care. The combination of high harmonic distortion, Butterworth, and fab 70's robot looks, makes it formiddable. Hifiman didn't make a stellar performer, but for a very specific sort of sound, it is pretty damn good. I've uploaded some RMAA tests of the HM601 driving no load,
Victor FX500, and
ACS T1.
Here are the RMAA tests of the HM601. I'll ad square wave performance later. Suffice to say, it isn't about performance, something the T51 sort is about. But where the T51 made some bad assumptions and stuck with them only half-arsed, the HM601 does a good job sticking to its guns. I'm not the real market for a player like this, but I like what Hifiman are trying here.
I wish the firmware was better, and navigation made sense.