On Windows, that’s VST2, which is likely to get ‘de-supported’ soon; so it’s probably best getting the VST3 plug-in up and running, which is single output only.
Also, if it’s anything like the Mac version, then the Reverb for all instruments is only passed through channels 1-2…!!
I certainly wish MakeMusic/Garritan would bring out a VTS3 multi-Aria Player for Windows as they have for Macs, but I am not optimistic. The alternative would be to use the single-instance VST3 Aria Player or just move on to NotePerformer and NPPE with other sound libraries, which I have pretty much done.
If you’re creating Endpoints in Dorico, then using separate VST instances for each Player makes sense, as then you don’t load 16 Brass instruments just because you’ve got one trumpet in your project.
Noteperformer doesn’t yet have the range of instruments that Garritan has, and there are still some decent instruments, mostly percussion or single-sound things. JABB brass and Saxes are very weedy and thin, but they are at least comprehensive.
I know. I used Garritan for many years with Finale and have most of the Garritan libraries.
Still, as I said, I wish MakeMusic would do Windows users the courtesy of providing a multiplayer VST3 version so users who migrate to other platforms (by necessity) can continue to use Garritan sounds.