Yes, its possible.
As long as they dont conflict, you can simply use a 3.5mm jack to 3.5mm Jack lead ( The same type as you get with a TV Card for example, to simply output from SoundCard A's Output, into SoundCard B's LINE-IN.
You can then use the output of SoundCard B only and have your swapping.
To be honest though, this way you will only really get the quality of the lesser card so havign an Audigy 4 means that you will be wasting your time in buying it I think?
To be honest though, I am in a similar boat in some ways.
My speakers ( Altec Lansing 955 ) dotn have Volume controls or headphone connections, so I have had to keep to the Audigy 1 because this alos allows me to use my LiveDrive from the SB-Live, giving me the Volume controls and jack for the Headphones, and the keyboard I use for the normal Volume controls... Can be shaky though cos if I just yank the headphones out of the LiveDrive, without knocking the Volume down, it can get a bit hairy when the doors blow off at 3am!!!