I really comes down to personal preference and price. If you have no brand preference (and trust me, those who do would gladly lose features and pay more just to say in a brand - think Apple for an egregious example of it), then go on price. Both are excellent receivers. It is impossible for the human ear to hear the difference between 24 and 32 bit dacs, so do not let that sway you. The Onkyo has better video processing capabilities - but I doubt most humans will be able to notice the difference in that, so I would not let it sway you either way.
EDIT: Also, 4K pass-through is nothing to brag about right now. Until HDMI 2.0 comes out we are stuck with a crippled form of 4K video. The current iterations cannot handle a 60Hz 2K signal at all, so the 4K pass-through is sort of a joke. By the time 4K is sorted out and we have HDMI 2.0, you will be in the market for a new receiver anyway...and new BluRay player...and new TV...
Basically, given the subtle differences between the two, if you do not have a brand preference then make your decision based on price.
EDIT: Fixed obvious error of saying 2K instead of 4K