Hi Lionstracs
I have done some research, and it appears that the ASIO driver specification only allows the use of 1 soundcard at a time, (However some soundcard manufactures have apparently hacked the ASIO driver to allow you to use multiple soundcards simultaneously) so I am afraid that unless it is supported by the soundcard driver it cannot be done with ASIO.
This is not a Windows OS problem, as if you use WDM drivers, you can use as many soundcards as you like simultaneously, and any quality sequencer program will see all the cards as one.
For further information pop over to the various soundcard manufactures sites.
Hope this helps

Bill