there is support specifically for each type of changer, currently the following ones are supported (if you look at the Powerfile_C200 code)
* Powerfile C200 (very expensive)
* Powerfile R200 (even more expensive)
* Escient (outside of most middle class budgets)
* Sony XL1B series
each one has specific support, and is predicated on a combination of mtx being able to manipulate the changer, and for the embedded drive layout to be programmed into the device driver for each device. The XL1B is especially different because the firmware is very brain-damaged from a typical changer perspective, there is a lot of assumption done by the official Sony software as to how the drive should act, and thus a lot of workarounds had to be implemented in mtx (the status data is completely different than your typical autoloader), etc.