Years ago I used KVM switches and a single monitor. That was back in the days when I'd also have paper databooks open on the bench. These days, more and larger screens have replaced paper documentation.
As I sit here, I have four monitors surrounding me... two 32in units on the main workstation, plus the laptop and its external 27in screen. All of the standalone monitors are wall mounted to free up the work surfaces below them. (The 27in is over the bench and has three power supplies and a function generator below it.) When I'm working on the bench all four typically have things displayed - IDE in debug mode on one 32in, docs (pinouts, schematics, etc.) on the other 32in, I/O support (Ethernet sniffers, CAN monitors, USB debugging, etc.) on the 27in, and often some sort of data capture going on the laptop's internal screen. Sometimes if I'm working on dual-firmware environments (example: developing hardware that connects to a smartphone), I'll have an IDE running on both PC's so I can monitor/step through the code on either end of the connection simultaneously, watching how each interacts with the other.
A KVM environment would be a serious step backward, at least in this environment. More and bigger screens is the present and the future!
The reason I was thinking software KVM, is it would allow you to display both computers simultaneously on a single monitor (data of unit B is delivered via Ethernet). Works great with a widescreen monitor; say 29" - 32" range. Not terribly expensive either if you've the monitor for it (or are in need of an additional monitor).
You've clearly got enough screens, but I'm not quite certain of what you're trying to do.
- For example, do you really just need to have a single keyboard that can access multiple systems?
- Or do you truly need to display information from 2 systems on a single monitor?
For disclosure, I've a 32" LG that has this capability (Split Screen software). Currently it's only connected to a single system, but I do see the benefit of additional units.
Currently I've 4 non-functional units that I may get lucky enough to cobble a working system together (IIRC, they needed motherboard repairs).