I can assume that you didn't like the SE5 ult because you didn't like the overall tone, specially in terms of balance between bass, mid and treble.
If you are looking for something linear/reference type, with better clarity and more treble sparkle, NT6 is the way to go.
Only two downside for me on NT6,
1. It's is still the brightest CIEM I have ever own, so it is bright, that's for certain. Although the treble is very smoothly presented, for me I still want to take rest from it's brightness time to time, unless the DAC power is there.
2. The bass is not as punchy as SE5 unless you drive it using a very powerful source (desktop ones), IMO an overkill powerful is actually good for NT6. My NT6 + hybrid 8 wire cable on Anedio D2 high gain ( I don't have it any more), it still one of the best sounding system I have ever heard, even better than SE5. But if I drive NT6 on my portable DAC, unfortunately the sound signature will shift to a slightly thinner, brighter, bass light one. This case, I will prefer SE5 ult over the NT6.