Dear Gerard,
Logic Express is indeed perfectly suitable for hosting our Vienna Instruments as Audio Units and I assumed that your local dealer, upon recommending the application for your purposes in the first place, would eventually support you with setting up Logic Express in order to fit your particular situation. In fact, it´s quite simple:
Please open the Environment window, either using the main "Window" menu or the (default-)keycommand Command-(aka Apple-)8, and create a "Channel Splitter" next to your Audio Instruments, then draw cables to 16 of your Audio Instrument channels, which have our Vienna Instruments instanciated.
If you are using the IAC bus, please also create a "Physical Input" along with f.i. a "MIDI Monitor" and route the IAC bus to the Monitor in order to avoid MIDI loops.
If you want to, we could send you a screenshot of how this should look like!
Best, Marnix
PS: If you want to import an environment into Logic, please use the "import layer" function in the "Options" menu of your Environment window - I just tested this in Logic Express from a Logic Pro 7.1 song without problems!