does anybody know how to play two logic or third party synths at the same time, while each keeping their independent parameters such as volume in Logic?

One easy way to do this is simply to record enable (hit the "R" buttons) on each tracks. Of course, you can also do interesting patching in the environment... including crossfading between sounds. You can see the TNT 303 tutorials by Steve H. for more info about this. [url]http://www.macprovideo.com/tutorial/logicTipsAndTricks[/url]