So before I have to return all the Noble demos, I did a quick comparison session just now with my AK120 as a source.
First K10 vs. K10 universal demo:
Although they sound similar, I will have to revise my previous first impressions of this comparison. The customs have more bass and more high end extension. They sound a little more forward in the mids and highs. I think part of the discrepancy is certainly the seal. I was using the double flange tips and even though I am getting a pretty good seal, I think the low end extension and higher bass levels are due to a better seal on the customs. I also feel like the differences in the mids and highs have to do with the fact that the tip of the custom is much deeper in my ear canal.The K10 custom definitely sounds better.
K10 universal demo vs. 8C universal demo:
The K10 has more bass level and extension than the 8C. The 8C is brighter. The highs are boosted slightly. The K10 demos are darker, but they still have tons of detail. The K10's are smoother.(As a side note, to me, the 8C demos are a lot different than the Heir 8.A's. The 8A's have a LOT more bass but the bass is a little bloated.)
K10 custom vs. 8C universal demo:
Now, the K10 bass level is significantly higher and bass extension goes lower. Even though the K10 customs have more high frequency than the demos, the 8C still seems boosted compared to the K10 customs. The K10 is darker, but I still hear tons of detail and smooth non-fatiguing highs.
Well that's some quick impressions. Hope this helps a little. Let me know if you have more questions.