I did see your post. That was in part what motivated me to get the survey going, actually. I do get that the input symbol (which is in common use, actually) is not well recognized. The gain symbol, I just made up, so I'm not surprised that nobody recognizes it. Schiit uses progressively taller bars, which makes about as much sense as a triangle.
Yeah the Schiit ones totally lost me when I first saw them on some of their gear.
I figured maybe the reason you settled on all-text vs all-icons is due to consistency, which could be an issue I guess. I'm aware you have a psych degree, so maybe there's a rationale there regarding visual consistency that I'm not aware of.
One idea regarding "all text" would be to just change "headphone" to "phone" or "phones", which is commonly seen on many amps that use all-text, which at least keeps all of the words smaller and evenly spaced apart, thus less cluttered. (if you're curious which of those two is most common, it seems to be the plural "phones", i see it on many high-end A/V receivers from top brands on google images.)
The switches are the latching pushbutton types, so I guess in theory I should accompany them with the "top hat" symbols showing the functionality with the switched depressed and released. I think that would just clutter the front panel, though. I'm a bit more of a "push the buttons until sound comes out" type in that regard. Besides, the "top hat" symbols don't make a lot of sense either. Not to me at least, but I've been wrong before.
Yeah those top hat ones are weird, I think those are also from AV receivers. I think there was a time when most people knew what they were since they were on receivers, but nowadays I'm not sure since they're a bit less commonly seen, and a lot of younger people have basic stereo setups with no receiver, and besides, all functionality is controlled digitally through menus and the remote control nowadays (or you'll have a simple softbutton with icons on the display telling you what you selected). I agree the top hats would probably clutter it up a bit, and honestly it's only the input that would be trial and error, I imagine it would be intuitive to think that depressed gain is low, and pressed in is high.
Based on what you've said about the circuit design being differential even for RCA input though, my *guess* for input would be depressed is XLR in, and pressed is RCA in, but since most users will probably use it with an RCA DAC, the opposite might be just as likely just for depressed being the most "common" use case.