I haven't heard the UE900 with pinhole blocked, but UE900s are much smoother and wider, and more natural. H-200 has more impactful bass and clarity, but with harsh edges. If you are looking for more intimate and aggressive sound, H-200 is a good side step from UE900. Personally, I much preferred UE900(that's because I'm a smoothness and neutrality head). Detail and soundstage wise, UE900 is better, but H-200 has better clarity and bass impact.
Thanks for the comparison! I have a pretty good idea of how the H-200 sounds like now. Sounds like a fun complimentary sidegrade from the UE900.
(BTW, with the pinhole blocked the UE900 will sound even more neutral and details will shine through better. I suggest all UE900 owners do the mod unless they like more bass.)