My computer

CPU intel i7-920
6 GB Ram
GeForce GTS 250

everything work awesome all the drivers working very good also the sound but have small issue
this computer do really hard things in video editing and 3d VFX but i feel there is very simple tasks can't do it good like listening itunes in background and just opening some tabs in safari (the audio stay cuts like has load and processing very heavy thing) while i am just browsing the internet

while if i look at the performance of the computer at this time

i found that used from the 6 g ram about 2g while 4g are free
cpu 94% idle and about 6 or 3% in use

while when i open After effects or any editing program it starts using the rams more and the idle parts (audio inside editing programs works great)

so why it don't use them if it needs more processing to make the audio tracks works without cuting cz i feel the cuting looks like it's trying to do alot of process and can't !
its just audio track what kind of processing don't know!

i notice that if i played the itunes after closing the after effects i feel it works good for a while even if i am working on safari then it starts to become lag and cuts again (only the audio everything else works great)

any help appreciated