I'm also happy with the IE900 stock cable performance, although I recently bought an Effect Grandioso (4.4mm balanced) that I planned to use on a UE900. I have been getting nice synergy with a hybrid cable on the UE, but I wanted a thin cable to use with it.After some tip rolling, the tips that works best for me, providing me an optimal seal and the best sound performance is the SpinFit W1. I am using the medium size. In terms of the cable, I did try the ddHiFi BC130B (Air Nyx) OCC Cable and did not notice a significant difference. If anything, the bass on the stock cable has slightly more punch. I am sticking to the stock cable!
Loving the IE900!
I found that it actually would fit with the IE900 as well and lo and behold I really liked the sound from it. Mids and highs sound a little more crisper to me. The soundstage appears a little wider as well. The bass is slam is still there.
So am sticking with the Grandioso on the IE900 for a little while longer. UE900 will have to do with my thicker cable for now. I tried the original IE900 cable on the UE, but sound comes out a little flat and dull.
Can't lie, but I think the cable looks really nice with the IE900 as well.