Pass Labs XP-20 using pass thru for home theater

I have the Pass Labs set up already for two channel stereo.
It's connected to a Pass Labs X350.5 amplifier driving my Vandersteen 5A's.
I also will be using a Arcam AVP 700 surround processor connected to another amplifier, driving my rear Vandersteen VSM-1 Signature surrounds.
The Pass Labs manual says to connect the right & left front outputs of the surround processor, to input 5/pass thru on the XP-20.
I would of thought to run the right & left outputs of the rear channels of the surround processor, to the pass thru/input 5 on the Pass?
Can anyone help me regarding this?