.sit is Stuffit, a totally lame and outdated mac-only compression format. Here, this should be easier:
http://www.quaketastic.com/upload/files/tools/mac/misc/eUtils_r10.zip
The codebase is basically the Quest compilers, but enhanced and fixed up. Like, the original Quest utils had their own pointfile format, but pOx reverted it to standard quake style. Some higher limits too (but nowhere near bjp-tools' level), better handling of complex geometry, and probably some other features I am forgetting right now.
Truth time: the detail brushes in the eUtils don't work exactly like Q3 engine detail. I have done tests and they split the BSP tree exactly the same as regular brushes. However, and this is the important part for this discussion, they are ignored by VIS.
Both qbsp and vis have to be aware of the detail brushes, but they definitely work in all engines. I'm no programmer, but I had a look at the relevant parts of the source, and it looked to me like the main change was a new contents type (sky, lava, water, slime...and detail), and all brushes in am_detail entities were given that type. Then vis knows to ignore them, I guess.