It's clear that the AOTC subs are the theatrical versions, while TPM, ANH and ROTJ were text streams. I think, if you had access to the original .TS recordings for those, you might be able to strip the subs out entirely with something like ProjectX. However, as they are commonly available, they're burned in.
Does anyone know if the original .TS recordings were ever available for either the german or british 1080i/p rips?