Zaheer pointed me to a temporary solution for my calendar sync problem while he (hopefully) keeps working on his more final solution which would allow full multiple-calendar synchronization.
I have a previous GooSync account that I used happily with my E51. GooSync supports SyncML, so it can be used with SyncEvolution on the device, which was recently ported.
I’ve put full instructions on my wiki if you’re in the same boat as me. Let me know if it works for you! And thanks again Zaheer for pointing the way.