I think the OP's question is a bit ambiguous. One's hearing may be physically impaired due to age, injury or whatever. But I think the OP means ability to differentiate between a merely good system and a very good system, i.e, one that is capable of producing realistic instrumental timbre, low level information, etc. As a trained musician and a past recording engineer, I've often wondered what non-musicians were actually listening to when they judged a system. I don't think you can ever know. But one thing I learned in my years of working in music - never assume someone else can't hear something just because you can't. IMO.
