I just finished "making" my custom in-ear head phones from http://www.earfuze.com/product.html I bought the Motorsports Fuzelite.
First impressions - excellent audio quality and fit. The "naked" headphones are short and do not stick out of the ear enough to allow the helmet to push on them as many other products do. Even without the custom fit material, these would be a great improvement over many devices.
The two-part material used to make the custom fit which blocks out ambient sound is color coded; I used red for right. The material is super soft and almost pours into the ear, on top of the headphones. The instructions tell you how to smush it down into you ear so it will hook on the part above the opening.
15 minutes of listening to tunes while it cures.
Once cured, the material is firm and very light. With a little experimentation, it's easy to put them your ears and remove them. I don't see any likelihood of helmet interference - putting on, removing, or wearing - as these devices are virtually flush with the ears. I couldn't hear the TV with the installed.
Seem to be very comfortable - a perfect fit for my ears. Not bad at all for $35.
I went out the garage and grabbed my helmet. No problem pulling the helmet on - Ear Fuze stayed in place. Absolutely NO pressure from the helmet on these headphones! The right one was pulled out when I pulled the helmet off - I think this is a learning issue and no big deal.
I give these headphones two thumbs up!
Update: When I tried these with the helmet, I noticed I could hear the TV; it was muffled quite a bit. Turns out the TV was muted initially :-)