I currently have an mbox 3 that I use with PT8, and a Saffire Pro 40 that I use with Reaper, and am going to make the jump to PT 10 or 11. I want to add 8 more input channels so I can adat/spdif/optical them together and get at least a simultaneous 16 going into PT. SUggestions for this and to stay below $750? (new or used) Also is it possible to string all 3 together for 18 channels?