I have some archives in ace so could be usefull. And playing cue sheet + fullalbum mp3 from archive would be nice too

Why not convert them to WinRAR, you'll get a little better compression to boot, probably.

If by full album mp3s you mean albumwrap, dont use those, from what I know they are a very horrible thing. I would advise you to use RAR, but Ill assume your sharing those .aces in emule or something.

thats it

One problem with ACE is that there are no sources for the decoding routines (like ARJ, RAR, ZIP...). You must rely on e-merge's precompiled DLL. It can't be compiled inside foo_unpack, and that would probably make things clumsy.

rjamorim's post pretty much explains why ACE isn't supported. also, i've looked into ace dll and their api is really bad (taking char* filename as parameter, can't support unicode filenames or propertly hook to fb2k file readers) and ACE support in fb2k would have unfixable problems.