So download JackOSX and open the app--Before you press the start button open Jack preferences and specify your interface(Ensemble,828, Built in Audio, whatever)-select your sample rate, start with a modest buffer size, give yourself a bunch virtual input and output channels.Tick the boxes relevant to you in the bottom panel.......
Start JackPilot before you boot Logic or VE .....
IN VE preferences select Core Audio:Jack Router and set the latency the same as you have it in Jack Prefs........
In Logic in your Audio Hardware setup(H?) Make your Device Jack Router and set buffer size(latency) as above.
In Logic , open your environment . open Audio in the top left, in the "New" menu, choose software instrument from Channel strip....Open 4 for now (WW, Brass, Perc, Strings). Choose an "External instrument" for these channels and set them to inputs 1-2, 3-4,5-6, 7-8. You can ignore the midi destination settings here, you will already have those channels assigned through IAC on your arrange page.
In Ve setup an instrument (presuming you have midi sorted on your IAC's) set it's output to 1-2(VE should be showing all your virtual channels by now)
Now, go back to your Jack pilot box and click "Routing" .This will open your connections manager box.....
In the left panel you will see Vienna ensemble and all it's possible outputs...In the middle Panel you can choose Logic and all its inputs.So...In the left panel click VE out 1, then in the mid panel click Logic in 1-They should both go red to indicate they are connected.if anything else goes red it means the audio will be routed elsewhere so all you need to do is click the offender to turn it off......
Connect your corresponding channels in the connections manager and save it as a studio setup(Thank Jayzuz it only needs to be done once!!!...)
Now , unless i've forgotten something ,you should have audio coming into Logic from VE through Jack....
Remember, you've got to start Jack first, then VE, then Logic....when VE has all your instruments open, then you open your saved studio setup.
On the Jack site there is a script to open and boot it on startup which is very handy....
Hope this helps!!!
Ray