This unit has been in my studio for a number of years. It works great and shows signs of normal use for it's age. I am downsizing my studio and downsizing my equipment so no longer have a need for it.From the Manufacturer:Similar in design to the M3, the TB4 provides facilities to act as the control room monitor source selector & adds a host of features making it a studio communications control module as well. The control room signal path is completely passive, with a four gang stepped attenuator, that tracks within ±.05dB. The TB4 includes an independent cue & talkback system with independent level controls, selectable headphone monitoring, microphone & remote switching.Features:Four balanced stereo inputs on XLRsTwo Balanced stereo outputs on XLRsStepped level control that tracks to ±.05dBEngineer's headphone output with level controlStereo Cue Inputs & Outputs on 1/4" jacksCue source selector and master level controlTalkback Interrupt switch and level controlThe TB4MKIII has been upgraded with a 47 position stepped attenuator made exclusively for Coleman Audio. The TB4MKIII is a control room monitor and communication module all in one. The main signal path is completely passive.with four stereo inputs to A/B signals and two stereo outputs for main and alternate speakers. There's a cue master level control and a switch that selects either the control room signal or a dedicated cue mix. The engineers headphone has a level control and can monitor the control room signal or the dedicated cue mix too.The cue input and outputs are on TRS 1/4" jacks. The talkback switch dims the control room monitors and feeds talkback to the cue mix. There is a slate output (i.e. take 1 take 2) activated by the talkback switch on the back panel just above the remote talkback jack.