Thanks for this thread!
The backwards bi-semi-flange-mushroom-thingy with a single flange silicone covering over it gives me the best seal Ive had with the IE8.
Stock tips that came with it gave me a lot of frustration: I couldnt get a full seal with any of them, the only ones that came close were the large foamies.
With this combination (as seen in Kwang411's picture) I get perfect seal and first time i really notice the midbass-bump. (needs a bit EQ'ing for most music).
Only downside is they protrude a bit further from the ears but not too badly. Comfort is ok, not perfect but good enough to wear several hours without problems.
I will still probably end up having custom sleeves made but until then this is a good solution.
I do wonder what Sennheiser was thinking when they designed the fit for these, cause other IEMs like my akg's I can just shove in and get a perfect fit/seal every time, but with the IE8 it turns into a serious challenge for me, which is pretty frustrating. I dont think my ears are very weird but I do think the ' flap' that starts at the face-side and goes towards covering part of the earhole is a bit larger for me then average. I guess that gets in the way of the rather large housings of the IE8, pressing them out of place enough to prevent a seal.