I'm not really sure, but since I had to custom make those cables through the floppy opening, since the IDC connector doesn't fit, I'm kind of committed!

Maybe I'll throw mmcmaster's SCSI2SD internally, use the USB to ADB adapter, and have the mega-SE. I still like the idea of using the SE as an initial step in bitbanging the PDS, since 1) it's 16bits wide, 2) it's slow, and 3) it has the connector allowing for easy access to the signals, so maybe I'll turn it into an experimentation box.