Please remove USE arts (and possible esd?) from your package as they have been deprecated wrt bug 270575. Or state in this bug that it's not possible if there is no alternative and it would reduce the functionality of your program.
It will still have good old OSS output, so no objection! I've removed current ~arch ebuild, and bumped to cynthiune-0.9.5-r3 (with arts and esd dropped)