How can I add more channels to my 16.4.2 without having to get another 16.4.2? I only need about 4 more channels for my current setup and don't want to get a full second mixer for this. My thought (if it's possible) is to have a second presonus rackmount interface for the drums, have them linked to the mixer and have them mixed as a sub group channel. I still want to be able to record all 20 Inputs into studio one.