OK, GB running on a iMac 800 Mhz. Everything is cool except for big time guitar lag. I am inputting with a Direct Mix USB 3 input device. I tried the preferences for Optimize For Better Performance- but neither of these fixes the lag problem. It is like a second or so behind. Why is this? What do I need to do to fix it? I really cant play along with GB this way!! Anyone have any suggestions?