2. ASIO. I guess this is new with 2.0. If I use this option will it have any affect on how 1.5 works? I'm not sure that I really want to stay with 2.0 at this point, though there seem to be some nice features if I can figure them out...
Using ASIO in 2.0 should not affect 1.5 in the slightest. They are different types of drivers, and both types of drivers can be installed at the same time. AA 1.5 will continue to use the WDM drivers, AA 2.0 will use the ASIO drivers. (This is all probably a bit of an oversimplification, but gives you the essence of what is happening.)
For example, just the other day I ran AA 1.5 on my laptop (where I usually run AA 2.0), because my external Firewire audio interface was plugged into a different machine. Not quite your situation, but an example of how the different AA versions don't interfere with each other.
BTW, your Audiophile 2496 is well-supported by both ASIO and WDM drivers. Well, at least my one is, and yours shouldn't be any different.