I almost exclusively run my S17 on high gain, 100ma mode because the sound is fuller, with more bass and the mids are really good, it brings them a little bit forward, so depending on your headphone and rest of the chain that might be a little bit too much of a good thing, but I will say that it's and amp that has meat to the bones, I can see why some people compare it to tube amps because now that I have one, I do see where they're coming from when they make that comparison, don't get me wrong, it's still an SS amp in it's character, but it has some of those tube qualities, good holography, great sound stage a a little bit more alive in the sound.
The S17 doesn't get dangerously hot, it does run hot but it's not something that it's going to harm you if you touch it, tho I wouldn't stack things both on top or directly on the bottom of this amp because if you have a DAC that runs also somewhat hot, like my Cyan 2, then it's not a good idea to add to the heat, it could potentially cause problems. If you get this amp and you live in a place that gets hot in the summer, then heat and temperature management with this amp is going to be something that your going to have to plan around this amp and the rest of your audio setup.