It's not the missing JVS board, it's the missing base board. That board has 2 micro controllers that handle the jvs io and force feedback serial io. They also interface to an eeprom memory chip, a real time clock chip and a 128 Kb non volatile ram chip.
The xbox kernel only run's one xbe. This makes it difficult to add code that runs in the background. So, you could patch a game and redirect it's jvs communication, but you don't have an easy way to store the subroutine with your new code. You will need to create a xbe with it that has it's own embedded "xbe loader" to load (and patch during load eventually) the game xbe.
firmware.asic is the firmware that makes the dimm load a game partition from either gdrom, compact flash or using netboot. firmware.bin and firmware2.bin are the firmwares for the 2 microcontrollers on the base board. Without a dimm, I don't think firmware.asic has much interesting.