If you mean "can two streams be listened to at once in Secondlife?" .. the answer is no.
If you mean you want to do a show with both of you on the same stream, that's an input issue .. you can use a phone patch from Radio Shack for the second person to call in to your PC while you're using a mike and you both can input audio to the stream together. You'd probably need an external mixer to mix the phone patch input with your mike. The mixer output would then go to your sound card Line In
(I'm also a Secondlife DJ under the name "BigJack Rolls"