Closeup of the rack. From top to bottom, left to right: M-Audio Duo 2-channel USB (and S/PDIF) audio interface (for when I need 10 inputs), Presonus HP-4 headphone amp, Symetrix 628 voice channel (wired via S/PDIF to FireStudio), Presonus FireStudio FireWire audio interface with 8 mic preamps, S/PDIF input, and up to 16 ADAT inputs (for future input expansion).