I have seen this behaviour very rarely. I think sometimes my code which enables ISA interrupts doesn't work properly on the Miata but I can't figure out a pattern yet. Try rebooting a couple of times to see if it unsticks itself.

I haven't had much luck putting non DEC vga cards into the 433au which I have. The SRM console barfs something about an invalid device and then halts. That might just be a firmware problem and I have only tried using an MGA Mill II as a replacement for the TGA card which came with it so your mileage may vary.

The boot process will detect which console is active automatically. You don't need any extra flags. There is an SRM environment variable 'console' to select the default ('set console graphics' or 'set console serial') but even if a serial console is the default, you can swap back to the vga console by hitting return a few times.

Don't worry about bothering me with details. I can't fix bugs unless people tell me about them :-)