Thanks for the response - I guess it's clear that I'm not particularly familiar with this.
very short list of explicitly supported boards.
Do you mean shields?
I realize now that I misunderstood the XmegaDuino github page, which lists a few boards that it works with (AVR xplain board, Sparkfun xmega100 breakout board, Magnetovore, Boston Android, couple others). I mistook these boards for individual microcontrollers and assumed this meant that XmegaDuino did not work with all Xmega microcontrollers. This is not what it meant, but I still don't know how to tell if XmegaDuino will work out of the box on all Xmega MCUs.
How do I know whether I will be able to get the ATxmega256A3B working with Arduino?
Do you mean you want to get this chip working with the tool chain (aka IDE)?
Yes - if use a PDI programmer to burn the bootloader, can I simply open up (their version of) the Arduino IDE, code as I would normally, and hit upload? Or am I missing something?
Thanks again for the help.