I think the RX-1 struggles a bit with electronic genre(this is sometimes more of a case for single dynamics). I personally think the cross-overs on the ZS5 separates the sound to provide more clarity. Perhaps you are into certain genres that the dynamic drivers do well in, such as violin for example. I think if you have a track that focuses mainly on a specific instrument I think a single driver dynamic probably has better performance and perhaps more natural sound? For well recorded music, I did notice that ZS5 acted weird, it doesn't resolve that well, and sound becomes smoothed or abstracted out in clumps. That doesn't seem to be the problem with the RX-1. RX-1 does have good sense of wide space, and ZS5's sense of space is different since sounds are more separated out, but the RX-1 sounds are even across the space. It does sound more realistic, and more textures to the sound.
I think for certain tracks ZS5 does well, but it's for electronic genre, and sounds fun. Clarity, dynamics, and quantity of bass is it's strengths, but resolution is not. If you are not into electronic genre, and listen to mostly audiophile tracks that are well recorded, classical, and vocals with lots of nuances, the RX-1 is the better choice.
Earbuds, at least with the RX-1, for recordings with wide stage, sound does get opened up considerably.