As above, just pick up a map when you buy your passes.
To get to the Champery WC track, go up Super Morzine, up the Zore lift to the top, ride along the ridge to Avoriaz, down into Linderettes and rather than dropping down into the bottom section of the French National, keep in the path down to the Mossettes lift. All the way to the top. Down the Swiss National, up the new Crossets lift on the other side.
As you get off the lift in front of you above you will see the lift station for the Planachaux lift out of the Champery valley. Ride towards that, and you should spot some black signs that say coupe de monde. That's the DH track. if you miss the signs keep an eye out for the chair lift down to the right. It won't be running, but the mid station is basically the start of the track.
If you go, make sure you go early, the big lift out of Champery can be a bit of a wait, and the lift back out of Crossets back up to Mossettes shuts at 4.30 I seem to recall.