When it comes to calling the init routine, are you allowed to set the accumulator (as well as X/Y) before doing the JSR? If not, then I would assume that the accumulator should be #$00, simply because a PSID has it set to that as well? (unless it's a set of subtunes) e.g. JSR $1000 and not: LDA #$00 JSR $1000
IMHO you don't have to assume anything if you want to use a tune on an actual C64 program, initialize everything you need. Or is this compo for .sid files only? I don't think so.
Any chance for 256b category as well? ;)