Sounds quality isn't really dependent on circumaural vs supra-aural headphones. The major complaint I hear with supra-aural headphones is that they apply pressure on the ears, which can be unconfortable. Sound quality, however, is largely affected by the drivers.
Will these apply much pressure on the ears? Many headphones use the earpieces to stay in place, but these are positioned by the Rift's straps which should be able to do it without pressure from the earpieces.
It's not just listening fatigue from sound, but the pressure applied to the ear-lobes. I have used circum-aural headphones that I can use for hours upon hours since they were very comfortable (no pressure) and were not too bright or forward that they caused listening fatigue.
Yes, I have a pair of Grado S60 (supra-aural) which are by far my best sounding headphones, but I cannot use them for many hours on end for this reason, as loose as I try to set them, they eventually become uncomfortable.
