Hope it's alright to 'advertise' this: I just came across a company who is making piano samples that will work in the ARIA Player. 

https://www.productionvoices.com/sforzando-libraries/

Production Voices has a range of different pianos, including a Steinway D, Yamaha CFX, classic Electric Piano, and some 'mood' effects. Some "lite" versions are even donation-ware. They are described as for the "Sforzando" player, which is Plogue's free player based on the same technology as ARIA. 

(You can even run Garritan libraries in Sforzando.)

Other developers making libraries for SFZ/ARIA are Karoryfer Samples: https://pulse.audio/developer/karoryfer-samples/

It's nice that someone is releasing new instruments for ARIA. (cough).

For the record, I have no relationship with the company: I'm just a user. I've tried some of the Lite versions, and they seem very nice.