Spacey, also sorry to hear of your troubles.
Spacey, FWIW, I think Trucker's mention of Jim Roseberry is a good point. If the other fixes end up not working, although it would cost a little bit, it might be an idea to pay Jim Roseberry for a short consultation - he does do paid consulting, or at least he used to. It might be one way to have a real chance of getting to the bottom of what is going on.
It well could be that something in your box isn't playing nice with something else. It could also be the software...
That said, I am also one of the 8.5.3 persons, albeit for somewhat unusual reasons - the customization they removed in the X series is something I have to have due to some personal RL issues.
For what I do, working in MIDI with orchestra sound libraries, it does well enough (though there are certain MIDI bugs I have had to work around in the past).
The things I really could use/need, sadly the Bakers have either removed, or haven't updated in over a decade. For now, I have no reason to move into the land of Xn. I'm just not very happy with the direction Sonar is heading, but on some of the issues, I'm very much in the minority, and that is unfortunately that.