Assign the tracks you want to mix from to the mixer using the Track button, and take all other tracks off the mixer. Hit Stereo and hold it, then click the track number you want to mix down to. This will automatically light up a linked pair(it doesn't have to be 7/8). Actually, it can't be 7/8 if you're going to mix to only one track. While still holding Stereo, click and hold the Select of the track you want to mix down to, then click the Select of the track that is linked to it. That should break the link and let you mix down to only one track. I've done it several times successfully. In case you don't already know, linking tracks automatically causes their pan controls to be set hard right and hard left. This condition persists after the link has been broken.
