Sorry to hear that @Geoff_Brandenburg.
We plan to release a new macOS build of appleseed without the SSE 4.2 requirement. Unfortunately this is a staggering amount of work and we haven’t had the time to do it yet. We will keep you guys posted here about our progress.
On macOS, appleseed.studio is renamed to appleseed-studio to avoid confusing the Finder and to allow double-clicking on the file.