Hello, Albert.
I've been using Logic 9.1 (sometimes) with VSL Special Edition Extended and Plus Strings articulations, and also, several download instruments. I also use Finale 2010 at times.
In order to take advantage of the 64 bit Logic, I believe you need to use VE Pro in 64 bit mode. You can use the 32 bit VE Pro, VE2, VE3 and VI, but Logic will need to load them with a 'wrapper' that allows 32 bit to work in the 64 bit Logic 9.1. Logic 9.1 will also load in 32 bit mode.
I have enjoyed seeing Logic 9.1 64 bit with VE Pro 64 be able to access much more of the memory I have in my Mac Pro (12 gig). I can load up quite a large set of instruments in VE Pro 64 using Logic 9.1 64.
However, if you use other instruments in your work, most of them will have to load in the 32 bit 'wrapper.' Also, I believe that when you load 32 bit instruments into Logic 9.1 64, we are subject to the oringal 32 bit limitations for that load.
Many things are not ready for 64 bit right now, but VE Pro is. Logic is the first one there on the Mac, so it may be some time before others follow along. I hope not...I keep getting older!
Mac Pro 2.66-12 gig memory, OS X 10.6.2, Logic 9.1, Sibelius 6, Finale 2010.
Dennis