Yeah I get the same issues with the arms of the glasses getting sandwiched between the ear and the head. You'll find most On Ears will have the same problem as they put more force on the ear itself. Like sonic I too put the arms over the top but I understand how you might not want to do this all the time. The Onkyo's actually have quite a low clamping force so you'd probably have even greater problems with many other On Ears! I even have a problem with the P7's and my glasses but strangely only the left ear, although they do seem to be getting better. If you can find a headphone with a lot of very soft cushioning then you should be alright. Sony's in general are very good, the XB950's were incredible! You'd totally forget you were wearing them! I haven't tried any of the later high end Sony's but I hear that they're pretty good so maybe worth a look?
Out of interest how did you find the sound out of both the Onkyo's and H8's? Always nice to hear another opinion!