We have gone through time and space, and frequencies, too, concerning handling mixing of tracks. Another option is stereo placement. If you put instruments in specific locations in stereo space, you could hear them better.
Anyone who has heard early Jimi Hendrix recordings know the strange feeling of hearing drums in one loudspeaker, and Jimi Hendrix playing guitar in another one. Those were the early days of learning how to use stereo systems. Later it become quite sophisticated, especially in the eighties and nineties. As a good example, the hip-hop monster hit “Chasing Waterfalls” by TLC has very elegant placements of instruments and sound tracks.
Now later it seems a lot of productions just make a big ambient sound mesh with reverb and ping-pong delays providing the stereo spread. Also, some mastering tools, such as Izotope Ozone, has provisions to spread out the audio by specific spectrum segments, causing an artificial stereo spread.
One reason, I think, is that with large systems you can’t just expect to hear stereo concepts that clearly, so with large club system with cross-over PAs there’s just little chance to do individual stereo placements. Another issue, especially with low end sounds, is that any stereo spreads caused problems when cutting vinyl, the needle starts to jump — one reason why bass and similar low end frequencies could not even have stereo chorus.
Anyway, for a quick easy way to have instruments heard, selective panning always helps, if nothing else, it could be automated so the panning moves from speaker to speaker. When working with stereo placements, headphones are really good. Just remember that enclosed headphones have one idea of the mix, if you don’t double-check with loudspeaker monitoring, you will get a false idea what is heard. This is one reason why I never subscribe to the idea of headphones only mixing/mastering.