Following up to my last post: Today Dantz released a new Retrospect Driver Update that supports the DVR-109. I hooked everything back up and fired up Retrospect; it recognized the drive immediately and proceeded to happily write to my 16x media. (At around 360 MB/min, too; not bad, although perhaps not the boost I was looking for.)
Now the only problem is the fan in the Bytecc case, which is fairly loud; I may have to move the 109 into my G4 tower if I’m going to be using it as the primary drive from here on out. Still, I’m happy to (eventually) get things working the way they’re supposed to.