I have tried (and failed) several times to save changes to the [new in MC33] Playing Now Popup dialog -- i.e. Tools->Options->General->Interface->... Playing Now Popup...
For example, I tried (and failed) to change the duration of the popup from its default of 8 (seconds) to 3. (Comes back showing as 8.) Likewise, I was unable to 'Disable' the feature. (Comes back showing as enabled.) I also confirmed that the popup would display for 8 seconds after changing the duration to 3 seconds and also disabling the feature.
The dialog itself does not have a SAVE button, so I exit the dialog by clicking its X (eXit button). Likewise, the General page does not have a SAVE button, so I exit the page also by clicking its X button. At this point MC33 asks whether I wish to SAVE my changes and I click the SAVE button.
I successfully disabled the Playing Now Popup feature in my 'Trial' version of MC33. The only difference between my Trial install and my licensed install is that I chose 'Audio Only' for the licensed install [whereas the Trial was installed using defaults]. I completely deleted the Trial install some weeks before installing the licensed version.
Aside: The bottom of the ... Playing Now Popup... dialog is chopped off such that the (unchecked) 'Show for Video Files' checkbox is obscured. I had to hide my taskbar to see the bottom of the dialog.
Note: I successfully changed the Tools->Options->Audio->Bitstreaming option to DSD [proving that some settings can be changed].
The attached log file includes the Benchmark results (at the top of the file).