Kowa are bringing out a version of their 1.6x adaptor for the 883 that's compatible with the 663/TSN 3 series, as well as the 820-series when used alongside the relevant EC1 eyepiece adaptor. Will retail at around £250.
https://www.kowaproducts.com/KowaSystemS-Extender/KowaTSN-EX16S/
They also look as if they're bringing out various "System S' digiscoping accessories compatible with older scopes. Sadly though no 663-compatible version of their wide-angle 25-60x zoom eyepiece...
https://www.kowaproducts.com/KowaSystemS-Extender/KowaTSN-EX16S/
They also look as if they're bringing out various "System S' digiscoping accessories compatible with older scopes. Sadly though no 663-compatible version of their wide-angle 25-60x zoom eyepiece...