Something is definitely wrong...
In Sonar 3 and 6, I can mix up to 5 live streams _with_ effects, with <=10ms latency. My audio machine is an Athlon XP 2800+, with an Audigy 2 ZS Plat Pro.
As suggested, make sure you're using ASIO, and have all the buffer sizes set properly.
Also, updated drivers?
Cheers