I've got 3 digital amps from Tact that take a spdif signal as input. They have their own volume controls. Right now I'm going from a mac mini to usb adapters to spdif to the amps and that works fine, but it restricts my choice of software to those that can decode 5.1 and route the resulting signals to the 3 audio adapters. I'm also not certain how the signal quality is being impacted at each step from 5.1, to decoded, to usb, to spdif. Would like to pipe out the unmolested 5.1 source signal to a box that I know is doing the right thing.