I think that we're all still working through a few beta issues with the OSX version of Vienna Ensemble. I'm sure the VSL guys will address some of these issues quickly and get a new build up soon, which will function more reliably.
I spent a few hours trying to get it to work in Logic 7.2.3 yesterday, and spent a long time staring at spinning beachballs of death, both when intantiating the plugin of VE and then when trying to load matrices into the VE Instrument channels. I did get it to work on one ocassion, but it's too hit and miss to be a workable proposition at the moment (IMHO).
Just to perhaps clear up a few misconceptions, from what I managed to work out:
1. Vienna Ensemble CAN be run as a plugin (some people seem to think it's only a standalone application). Just as with the Vienna Instruments plugin, when you intantiate VE in Logic, it launches a standalone server application, and instead of creating an individual interface for each instrument, creates a single Vienna Ensemble interface, in which you can then load a whole collection of instruments, route them flexibly, and insert plugins. Midi is routed automatically from Logic to Vienna Ensemble, and audio is automatically routed back to Logic.
2. Setting up the MIDI side of things in Logic is exactly the same as for any other multitimbral virtual instrument. Some people seem to be under the impression that special Environment gymnastics are required - they're not. Just creat a 'Multi Instrument' in the Audio layer of the Environment, and cable it to the Audio Instrument channel which hosts the VE plugin. Then enable as many channels on the Multi Insutrment as you need (by clicking on the 16 buttons) and set the Audio Instrument with VE inserted on it to recieve MIDI on ALL channels. Same procedure as for Stylus, Kontakt, Halion, BFD .... etc. To play the instruments in Vienna Ensemble, in the Arrange Window you then select the Multi Instrument you created, NOT the Audio Instrument channel. ie. if you named the Multi Instrument 'Vienna', that will appear in the 'Audio' sub-menu when you click on the track in the Arrange Window.
I'm sure that makes it sound more complicated than it actually is. To me, Vienna Ensemble seems pretty straight-forward and well thought out, and the issues stem more from application instability than from design shortcomings, and I'm sure these will be addressed as soon as VSL are able to do so.
Jules