Forgive me for asking, as I haven't tried using one of these summing boxes: If you have more than 16 tracks, do you sum the external summers, or submix in the box using the mix engine you're trying to avoid? This is one of the things I haven't quite understood about the "summing box" rage. I typically send each mono track out to its own d/a and then to its own channel...just like a tape deck. I've never particularly liked the sound of mixing or submixing anything in the computer, but I'd think an external summing box would need 24-48 (as many tracks as your project has) inputs before it did all the good it could do by totally avoiding the mix engine in the box.
-tom
