Indigo has better bass texture and quality imo, the Elysian IEMs bass are nothing special. It’s quite dry in comparison and doesn’t have that great of texture, the sub bass tuning on X is great though. It digs deep and slams very hard when called for, I do find it’s too sub bass emphasized though. There isn’t enough mid thump for me and occasionally the sub bass can bleed.
X has a bigger stage on all planes but the separation on Indigo is better. Indigo is more in your head but it never comes off as congested. I think indigo has my personal favorite staging to date. I like big stages but not at the cost of cohesion and the X can be a bit disjointed at times to me, particularly between the lower and upper mids. With that said, the X won’t leave you wanting more on imaging ability either. It’s definitely top notch, I just personally feel indigo is in its own league there.
There is more upper mids in the signature on X but they’re presented in a laid back manner, they aren’t overly forward or imaged crazy up front, but there’s a lot of energy there. Hopefully rhat makes sense.
The Elysian stuff has the best treble in the game for EST drivers. It’s smoother than indigo and more extended but this can give off more of an ethereal sound.