On the ePot V3Max
1) Is there anyway to get the output attenuation and balance values, in addition to having the OLED installed? I was thinking of other graphical displays run by an Arduino, etc
While it hasn't been published, the V3 Max has a collection of commands etc that can be sent to the Max via UART serial communications. The Max also sends out commands/data via same UART. Each Max actually has a pair of UART channels allowing for independent downstream and upstream data exchange between boards or external devices. This system could be adapted to provide sufficient info for an external display or even control center.
2) In dual mono, balanced configuration, can the serial connection drive the data across a 6 foot cable?
Probably. It uses standard UART type communication via a 2 wire serial data link. If 6 feet proves too long for reliable comms the baud rate could be reduced to make it work.
3) In a balanced configuration, the Master board has to be the right channel. If I wanted the Master on the left, would the only difference be the remote's balance inputs would be reversed (push left to increase right)?
There's a lot of detailed bits in the code that depends on the primary board being the right channel. It would be hugely inconvenient (lots of time rewriting code) to flip this around or make it selectable. Some things are they way they are and we adapt accordingly. This is one of those things.