Can someone explain why this would be useful for me? I typically run a cardiod pair and a MS pair. The two are never close to being the same levels, really ever, especially the mid and side channels. Why would I want to control gain on 4 mis-matched channels by just spinning a single knob?
I was happy to see that with the firmware update using the front panel knobs for gain, I can link channels 1/2, and then separately link channels 3/4. ISO (front panel) Knob 1 controls 1/2, and ISO (Front panel) knob 3 controls 3/4. That is exactly how I have used my Tascam DR680. I do not foresee ever linking all 4 together, at least not with my mic combos. I did not think to check if there is an option to link 5/6, I'll have to look at that tonight.
There is a specific linking option for m/s, so you could balance your M/S and control that with ISO 1, and then control your cardioid pair after balancing on ISO 3, so you would have 2 master balance controls instead of 4 separate controls.