I think that the tips that come with MHC1 are wider bored compared to sony hybrids, right? use them on XB90EX too :) or you could get Meelec tips, one of these:
currently I'm using tips that came with my able planet and are really similar to the meelecs' but meelec tips are even more comfortable, because of the more bubbled shape :) as for meelecs, someone said somewhere here that clear tips are better for treble response, so I would get those. heck, I'd get those tips ASAP, just saving for the JVC FXZ100
almost forgot - I asked the same question about foam tips and people here didn't really recommend them - said that they are bad for high frequencies...
I disagree about the meelec tips. I bought the clear ones and when I got them, they fit loose on the xb90ex.
It's true that the bore is wider but the part that fits on the nozzle of the iem is also wider. It's actually about the same size as the ones that come with the fx40.
I'm not the kind that spends money on tips. I tried that just to make the xb90s worth it.
They did open up the sound quite a bit. But like I said. The fit is loose so it ended up stuck in my ear when I pulled out the xb90s just like the fx40 tips. After that one occurrence, I simply took it out, cleaned them, and put them back in the plastic bag. They're sitting in my drawer. So are the xb90s.
Here is a link where H2OFidelity explains how to fix the loose foam tips problem that you are talking about:
You do that and you may get a tight fit on those foam tips that otherwise would have a loose fit.