The Coda has greater resolution, a wider soundstage, and better instrument separation. Also, it’s more refined and has greater decay as mentioned earlier.
FWIW, the JC5 is merely an A21+ with a slightly altered bias and better quality parts. Both the JC5 and A21+ measure worse than the original THX-rated A21, and it’s definitely audible in real world use. The newer Parasound Halo amps are a regression in performance despite the claims of the spec sheets.