Just upagraded to X3 Studio, when I go to select Pro 24 as audio device it is listed but grayed out and does not allow me to select. So, I cannot hear any audio.  Any advice?

If running ASIO driver mode disable any other input and output device. The ASIO specification permits using only one I/O driver at a time.

Go into Device Manager and make sure the interface shows up there under Sound, Video and Game Controllers. If it isn't, then Windows doesn't know about it and therefore SONAR can't talk to it. That would most likely be because the driver isn't installed properly. If it does show up in Device Manager, open the Sounds control panel applet and see if the interfaces is listed there. If not, it could also be that the driver isn't installed properly. IIRC when I installed my Saffire there were actually three separate drivers that had to be installed (audio, MIDI and S/PDIF).
 
I'd also check that the firewire cable is seated properly at both ends.