iTunes Plus without iTunes?

I'm trying to replicate the iTunes Plus setting using another program like Max, but when I use what seems like the same settings (256kbps VBR), the files always turn out a fair bit larger. Can anyone help me make iTunes Plus files without using iTunes?

iTunes Plus is 256kbps VBR. I have no idea what the rest means though. Is it possible to replicate with an app such as Max or XLD?

Yes thank you for that though I'm looking at the iTunes plus encoder settings which you can see uses VBR. The store files may be different.

EDIT : Besides CBR would make even larger files than I'm already getting.