It would have been nice also if the unit would have automatically send mono to both left and right channels if only one of the input jacks were plugged in.

I was surprised to find its decently loud (not ear bursting like the presonus), quiet, compact, and users can listen to two separate tracks (2 pairs of 1/4" mono inputs on the back, a button next to each headphone port selects channel A/B, each channel has separate gain and balance controls too)

Both run on ac adapters, but this one has separate inputs for left and right channels or you can use just the left one for mono, plus it also allows 2 input sources which are switchable on a per user level

I put it back together and all four channels are working again