[KevWind]

I'm not sure I really get the question? Especially since any good mix on my home stereo or studio system sounds fine (albeit less dynamic) on my I phone even with just the built in speaker. Guess I'll have to listen closer.

And maybe I have not been paying attention but everybody I see listening on ear buds has a pair?

And when a playback system is actually putting out mono isn't it just putting putting both the L and R into one combo output?

The only thing I have noticed about trying to get a mix to sound good on limited playback systems is if the mix has lows like a kick drum or bass gtr. you seem to loose everything below about 150 hz so I tend to boost 100 to 250 a bit to keep the low instruments still audible