They fit pretty well actually. The EX71 sleeve is a lot grippier than the one that comes with the Apple In-Ears so it certainly doesn't slip out. The Apple In-Ears sound much better (cleaner, brighter and more defined) than the EX71s so putting the 2 together is almost the perfect combination.
The problem is that it doesn't look so great, and I have found that when they are not slipping out then the Apple In-Ear sleeves actually give a better seal than the EX71s.
I'm bumping this because I got a chance to try it out earlier.
The word "wow" would be an understatement. The Apple in-ears sound SO much better with Fontopia sleeves. I was extemely disappointed with the Apple phones and hadn't been using them; the bass was okay, but they were slightly tinny (cymbals sounded especially bad) and it was hard to get a good seal, especially in my right ear. The Fontopia sleeves correct both of those things. They stay in great, providing much better isolation and they make the headphones sound remarkably better; the "tinniness" is virtually gone. Even better than the Sennheiser PX100s I'd been using.
If you were disappointed with the Apple phones, but can get your hands on some Fontopia sleeves, definitely go for it.
Hey! I just talked to a Sony rep and he directed me to a place to order the EX71 sleeves. If you want to try this out, you can grab a set of EX71 sleeves for around $6 to $9 each, but you have to know what size you need!