Yep that's the only Aria selection I have in my custom list - the Multi one. The other one I never use it since I always load multiple instruments, each to its own output.
And I have the same exact selection as you have in the screenshot (+ "Ask Every Time").
If I load Aria Multi in X2 - same settings, same everything as X3 - all outputs load as per normal. It's only in X3 that I only get the first 2 main outs that's why I'm baffled.
Also, X3 is taking the same dll file that X2 is using (C:\user\program files\cakewalk\vstplugins\garritan\ARIA Mutli_x64.dll)
As I said in the OP, going into - Plugin Manager -> Plugin Properties -> Details... - X3 'sees' that Aria Multi has 32 outputs. But if I load the synth, I only get one synth track and one MIDI track. In the Aria Multi instance itself, the out channels (3/4, 5/6, etc...) in the dropdown menu are all grayed out - except of course "1/2".
I apologise if I was unclear and I hope this clarifies a bit.
Thank you for your input :)