I joined just to post to this ancient thread. I found it while searching for information on the serial data port on my Bose Lifestyle 35's AV28 Media Center. One of the earliest posts mentioned that it was possibly used internally by Bose for programming, and that was the conclusion I had come to.
I had wondered how one would go about replacing the DVD-ROM with a different model. Mine had a problem that seems to be very common in these: a slipped gear was preventing the eject from working properly. It's possible to repair the gear or replace the drive with the same model...
BUT, I got to thinking about how one would replace the DVD-ROM with another IDE model from the same manufacturer, or even one from a completely different manufacturer. The driver is built into the firmware most likely. And firmware updates come on (bootable, unknown OS) CD-ROM. Assuming you could figure out the format of the CD for the firmware update, how would you replace the driver for the DVD-ROM while you're using the drive? (This is a "chicken or the egg" type of question.)
My thought was that you couldn't do this via a CD-ROM update, and that you'd have to be able to bypass the DVD-ROM entirely and write to the PROM chips in some other way. That's when I said, "Aha! The serial data port!"
So the question I have would be how to use the serial data port to do firmware updates. Specifically, how is the data stored in the PROM chips? (What is the OS, file system, etc?) And how would you replace the driver for the DVD-ROM so you could replace the drive with a different model? (You'd have to be 100 percent certain about what you're doing, because this is definitely the recipe for turning your Lifestyle into a brick, if you aren't careful.)
There are people selling this drive for upwards of $400, because they know what they have. If you could find a way to update the driver via the serial data port, you'd have a wider choice of replacement drive options.