The PreSonus HP4 is a compact headphone amplifier with one set of stereo inputs and enough headphone outputs for the whole band. Each headphone output has a separate volume control, as does a rear-panel set of monitor/thru outputs. When you're checking phase coherency during mic placement, flip on the Mono function to really hear how it all folds down. Compare prices on new & used HP4 headphone amps on Reverb.com and find the best deals.