It’s not possible to ‘command’ ARIA Player to load particular samples from another app, apparently. So, at best, a Playback Template for ARIA will:
load one or more ARIA players as VST Intruments;
assign the Players to the VST and give them a channel number;
set the correct Expression Map for the instrument type.
I’ve started to create the necessary files to do this, but it’s currently limited to a small range of instrument types (standard Strings, most Woodwind, trumpet, vocal parts, organ). Other instruments will not be assigned VST/channel/map. It is still “fairly experimental”, and note that if the data isn’t correct, it will stop Dorico from launching!
At least, it means the only thing I have to do is to load the samples into the correct channels in ARIA. (Plus or minus separate output channels…!) You can of course save ensembles of instrument/samples in ARIA for use in multiple projects, or use Dorico project files as ‘templates’ for new projects, with ARIA already set up.
It’s likely that Dorico in the future will provide improved template functionality for all kinds of players.