m2kio, I'm using 10.3.9 and I do have CarbonSound.h: /System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/CarbonSound.framework/Versions/A/Headers/CarbonSound.h
Did you use a Finder search to try and find it? Annoyingly, it's hard to get the Finder to search in /System. You have to add it as a Specific Place. The "locate" command at the command line found it instantly, though.
Also, are you using wxMac 2.6.0 as released, or are you using more recent cvs versions? Given that filefn.cpp hasn't changed, I can only imagine that the change is due to changes in wxMac. I suppose another possibility is that your system is acting flaky and is spontaneously losing track of files. 8o
The problem with wxMac 2.5.5 is Xaignar's fault. For a while, aMule was maintaining several copies of some wx files (listctrl.h, listctrl.cpp) to work around various compatibility problems with the listctrl files that come with wx. With wxMac 2.6.0, Xaignar was able to eliminate the extra copies because wxMac's version was finally useable. Unfortunately, that means that Mac aMule now requires wxMac 2.6.0.

So, let's concentrate on identifying and fixing the performance problems.