the squeeze box player is working in .35, but we don't use sw clients to work with slimserver, i think one of the programmers used an emulator when he worked on squeeze box.
but i don't know other details, like what he used, i just remember seeing him once playing.
I'm playing same stream on two SW clients right now (1 slimp3slave in Core and 1 squeezeslave on win32 on laptop).. with latter you could easily try if it syncs with HW SBoxes.
It seems that there are major steps taken in relesing "sync" magic secret to community.
Author of softsqueeze SW client is tired of having problems with Java, so he released slimslave library in C :http://forums.slimdevices.com/showthread.php?t=20160&highlight=multiple
If one of your guys could take a review and merge it into Xine player (there will be some enhancements in that code) - then I guess we'll get SW squeezebox clients that should sync to HW players...
I also figured out how to run more SW clients on same IP (for implementing idea for multizone audio from Core) - you just send different virtual MAC addresses to slimserver and it distinguishes between them....