I first purchased the Sound Devices 664 for my work on Harvest with Cageny Gentry. I love having 6 mic preamps available for boom, lavs, plant mics, and environmental sounds. The 664 puts multitrack recording and mixing in one unit with plenty of outputs for cameras or communications. An innovative feature that Sound Devices added to the 664 is that one can take the direct outputs for inputs 1-6, and change them to line level inputs for an addition set of 6 tracks, channels 7-12.