QoS - 3036 router with VPN for NBX phone 1

[engjohn]

I am a little confused on how to properly implement QoS for this setup...

DSLModem <-->3Com3036<-->switch<-->NBX
|
|VPN to site B
|
DSLModem <-->3Com3036<-->switch<-->3102Phone

The VPN is a GRE in IPSec tunnel for full NBX functionality.
The question is, how do I have the router prioritize the NBX traffic over the VPN so that uploads or downloads on the DSL's do not slow down the NBX traffic?

The difficult part for me to understand is that, the traffic is over the VPN, so should I priortize the NBX traffic or the VPN traffic, or both?!?
Also, with the speed differing between upload and download (say 6MbsDN / 480KbsUP)
What is my best option...

Thanks!