Can you really expect Onkyo sound quality to go up with higher end models? I have been dealing with Onkyo in my home environment for a few years now and my reasonably solid impression is that Onkyo is just budget all the way.
Like, they have two kinds of bluray-disc-players, a really really really really REALLY budget one that can't even compare to Sony or Philips, and an expensive one that costs 4x as much and would have the appearance of being "high end" but as far as I expect it, that is just farce, it may be twice as good but will still break, it is just a thing with good features and other than that in the end you might find that it is still crap.
Naturally, my experience is extremely limited. I just had a dvd player (DV-SP506) break on me after a year, and instead of repairing it they gave me my money back, hoping I will buy the expensive BD player. If they had any inkling of reasonability they would introduce mid-range models and just drop the lower end ones. People buy the lower end ones not knowing what they'll get and then having to upgrade after the fact anyway, now owning a Onkyo receiver that will only look good with that Onkyo BD player, the BD-SP809 at €400. My local dealer plays into it by pretending he doesn't know and keeping silent about these issues unless you come back to him and express yourself and then he's like "oh yes, yes, that's right." Onkyo just plays a nasty business in that regard.
Is just my opinion.
Onkyo also creates CD players with digital outputs that you can't use on their receivers because the CD player switches to PCM mode on the digital channel at the same moment the CD starts playing, causing you to miss the first second of playback, rendering the feature completely useless. Of course they know this, but they are hoping to sell to unsuspecting customers.