Ive tried many set ups, but the simplest seems to work best. I can cope with 3 scanners, 4 might be tricky. For my set up i use a 3.5mm to L/R RCA cable, with mono RCA to 3.5mm connectors into a scanner each. That feeds a set of in-ear headphones, with true left and right signals to help reduce mental overload and help figure out what I'm hearing. I then have a headset that sits over both ears fed by a 3rd scanner. I usually run this stereo to help pick up the 3rd scanner transmissions (it's rare that all 3 scanners are open simultaneously). You could use a stereo headset with a L/R split in the same way in use my in-ear headphones to get 4 feeds?