Hi,
Even if you could run two sessions, one for each LOGIC, you can't compare that to a 16 channel unit.

You want the state of all signals to be samples at exactly the same time, I'm pretty sure having two separate LOGICs won't allow that. Even if two 8 channels units was able to connect a single session used in 16-bit mode I don't think it'll work due the (small but still) buffer that is inside LOGIC. It's not going to stay in sync and if they don't it's pretty useless.

/Henrik.