I discovered this late last night, a very highly configurable MIDI routing engine that lets you filter and route between any number of hardware synths and controllers.

http://www.bome.com/products/miditranslator#

I installed the trial version, used it for about five minutes then pulled out my credit card and bought the full version. Now I can launch into my keyboard rig without waiting for Cubase to start up, creating a new project, setting the tempo, creating all the tracks, I just hit my controller keyboard and everything works. Note on/off, controller data from a Novation master keyboard plus clock from the JD-XA gets routed to all my synths and effects and it took me about ten minutes to learn. Highly recommended - I'm not ion any way associated with the company, just really pleased to have found a great product.

I should add that there's a less feature-laden version which appears to be effectively free to non-commercial users, the author only requests you send him a postcard ...

http://www.bome.com/products/mtclassic

If you use hardware synths and want to do some poking under the hood with MIDI data then it's the best I've found. And I've done a lot of searching for something like this.