How can I tell iTunes to buffer more songs?

I use a local iTunes library BUT remote files. I told iTunes, that my iTunes Music/Media folder is on my NAS that I can access via Airport Extreme over WAN.

The problem I have is, that my connection has good upload and iTunes can play all files without buffering BUT it only buffers one file at once. When I click <Next Song> I have to wait for 2-10 seconds until iTunes loaded the next file.

I hope that iTunes can better. It has a "up next" function, why not load the next 2-3 songs while I am listening to the current song?

Can someone help me with that?

Thank you!