1) Open Audio Midi setup in Applications>Utlities
2) Click the Audio Tab. Now go to the audio menu item and click on Aggregate Device option
3) You need to create a new aggregate device so click the plus sign and name it - myAggDevice
4) Now in the list below, first select your audio device (in my case my apogee) and click the use checkbox and then select soundflower and select it's use checkbox
Thats the audio setup!
Now to setup the midi
1) Click on the midi tab in the Audio Midi setup
2) Double click on IAC Driver object
3) In the properties box add two new ports, call them Strings and Brass etc
4) Make sure the device is online and hit apply.
Now setup Vienna Ensemble
1) Open VE
2) Open Preferences and select the aggregate device under the audio tab
3) Select the IAC ports you created under the midi tab
4) Now create your vienna instruments, select the IAC driver under port dropdown say Strings and a midi channel. At the bottom of the mixer channel select the output channel.
This is were it gets a bit tricky. The first channels in your aggregate device relate to your audio device, the rest to soundflower. So for example you have a two channel audio device then outputs 1-2 will be your audio device, outputs 3-18 will be soundflower. So inside VE route your outputs of your instruments to the soundflower channels not your audio device.
Finally, set up logic!!
1) Open logic and set your audio device to be the aggregate device.
2) Set your main output channel to outputs 1-2 etc for your audio device
3) Create a new external instrument, set its output to one of the IAC's you created for example strings.
4) Then as you normally do, use the option create with next midi channel, these midi instruments will now be sending to the external VE
*Warning - in the enviroment you must not use the SUM option in your physical Input device as it will cause a loop. Therefore go to you clicks and ports layer and cable from your keyboard only to the sequencer input
5) To get the audio back in, simply create a aux track and set it's input to match the channel numbers that you had set in the VE. And set it's output to the master output channel.
You should now be able to send midi out of Logic to the VE's running and rout the audio back into Logic to process.
Hope this helps!!!