That's a bit like saying, the original Apple Macintosh II (on a 020 processor) is a tad slow, but if you drop a DayStar PowerCache 030 50Mhz into it it'll run a lot faster! You don't need to be a rocket scientist to figure that out really.
The Visioneer Paperport Vx scanner as purchased in it's entirety works via a serial connection. The software it comes with works via a serial connection.
How do I know this? I have one and it works via a serial connection.
I also have the SCSI adapter for it but that's an add on and did not come as part of the original Visioneer Paperport Vx product which works via a serial connection. You need a separate set of drivers for the SCSI adapter to work and it does not come as part of the original PaperPort, which works via a serial connection.
Have I made it clear that the PaperPort as it would have been originally purchased and with its original software works via a serial connection?