Right.
You will be sharing preamps, obviously. There are 3 ways to do this:
1) You both have preamp control. Either of you can change the preamp, but the change is for both desks.
2) One has preamp control, the other has automatically following trims using gain tracking. However, you only engage gain tracking after soundcheck, and there are caveats to whether this works well in practice
3) One has preamp control, and you don't gain track. The other manually adjusts trims as needed.
Personally, and maybe controversially, I would go for option 1 or 3. Here's why:
Gain tracking only works when you want to avoid the changes to preamp gain being made by the other engineer. However, sometimes you need those changes (like when an input is clipping), and so it could be handy to have one engineer fix that problem for both.
I think you just need to agree a gain structure between the 2 of you. Lets say you want your inputs to hit -18 on peak (arbitrary number). Both of you adjust preamps to maintain those levels as needed, and everyone is happy because you've both built your mixes around that gain structure. Either engineer can fix a clipping input for both. Simple.
I don't think mixing on trims is actually any quicker, and bad gain structure is always the start of a bad mix :-)
