Your position that "those who make testy arguments about differences is sound quality" will "need to prove those 'differences' exist" is only one side of this coin.

Since you have not compared the 990 to any other units out there, I have to say that those who make testy arguments about NO differences in sound quality will need to prove that they do not exist, by the same token.

You may not find the 990 well suited to your personal needs, but why belabor the point?
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--Greg