The 13 is not harder to drive. It's a couple DB less effecient (116 vs 118) but still very efficient. It has fewer drivers to control and is a higher impedance (28 vs 18) so DAPs are more likely to control it and not change character as much from damping factor issues. Both should be fine for most DAPs and improved with amps but if one needs an amp more, it's the 16 more so than the 13. Another aspect is that if your source has some hiss, the 13 should show over 3 db less due to the combo of impedance and efficiency.
Tonally, I prefer the 13. It doesn't have any extra sparkle or midbass but that's preference. The rest is just physics. It may be more critical of source by having less of it's own character. It has nothing to do with drive capability. Feed it well and you'll be rewarded.
Technically you may be correct, but my ears tell me different.
Straight out of a DAP, the 13s sound thin compared to the 16s - maybe that's the extra bass of the 16s making them sound richer?
However, plugging the 13s into an amp definitely changes the sound to my ears - it becomes lusher and fuller sounding.
Btw, does anyone know how much JH Audio charges to refit your CIEMs after the 30 days are up? And are you allowed to change the design of the shells?
Do you mean a minor adjustment or complete reshell? Minor adjustments have been free for me.
I think I read somewhere that a complete refit or re-design of the shells would be the same cost of getting new IEMs