I think the licensing is likely to trip me up.
Looks like a bespoke license including:
"You may not copy, reproduce, republish, download, post, broadcast, transmit, make available to the public, or otherwise use the Site content in any way except for your own personal, non-commercial purposes although you are permitted to make links to the Site content from your own personal web-site. You also agree not to adapt, alter or create a derivative work from any content accessed from the Site except for your own personal, non-commercial use. Any other use of the Site content requires our prior consent in writing. Content of the Pianobook Library is subject to the terms listed above."

I think that leaves only the option to try to get something working under HISE and then if anyone wants to build a personal binary they can, but wouldn't be able to release it in any form on the site. I think others have mapped individual instruments using SFZ. Another environment I have absolutely no knowledge of...

Thanks so much for your help - incredibly useful!