ices-cc doesn't support AAC, and given its developers' lack of interest in its future, it probably never will.
If you need AAC support, you'll need to use ShoutCast DNAS2 with sc_trans2. Aside from its comparatively high memory usage, DNAS2/sc_trans2 are comparable in quality to IceCast/icescc so there shouldn't be much drawback in switching.