The Monarch MKIIIs were famous for its stunning bass and resolving capability, but some disliked its peaky brightness at some higher frequencies. The Jupiter fixes all of that while adding a heft of mid-bass body making away the trend of nowadays iems' rather thin mid-bass response. The result is a set that replays in everything the MK3 does well while subliming all low frequency instruments to the point where it almost sounds speaker-like. The tamed mid-to-high-treble response compared to the MK3 rather makes that airyful upper treble extension (thank to the four ESTs I suppose) shine as if it can handle infinite amount of complexity while still maintaining that spaciousness, rendering the soundstage as if it's boundless as an abyss...All while still not losing any details that could ever be retrieved in a set of IEMs at a price like this.
Granted, set is almost $600 more than a base set of MK3, but for anyone who's listened to the MK3s and find it rather fatiguing over time, or just trying find that last bit of refinement to the overall presentation of the sound— This is the definitive set to go.