I don't know what did the AROS team change in the sources (I will look at them when I have some time), possibly compiling the muPFS-AIO can work 'out of the box'.
Only difference between aros and official pfs3 svn is that aros version includes "aio" support code (KS 1.x, access mode autodetection etc..) and needs aros compilation environment. EDIT: only reason it is in aros tree: KS 1.x compatibility without invasive changes to core pfs3 code requires preprocessor tricks that is easy with aros compiler system.
Official pfs3 is "plain" pfs3 and can be compiled with sas-c.
I probably didn't include mufs support because it does not make much sense in aio version. (very rarely needed)