How to decrease overall CPU usage on iMac?

Hi guys,

I purchased my first Mac ever, the iMac with 3.06ghz, 8GB and 1T.

I LOVE THIS iMac.

Now, I got this iMac to use Protools with plugins. Now I'm only using 3 tracks with virtual instruments and is already asking me to increase CPU usage or remove RTAS(virtual instruments).

Is there a way to chip off CPU usage from other programs that the computer may be using? Anyone has solution except removing some virtual instruments, I mean I got this iMac to work with music.

Thank You