Gary, a copule more thoughts. The Nikon 4000 I would think is a very good scanner. You said it is in good condition. I suggest you call LSI sales, make sure you are talking to Kitten, tell her your story and ask if you can get a loyal customer discount. You might be surprised.
If the 1680 scanner will not work on the latest OSX, do you really need the newest OS? Mark himself is still on El Capitan, which does have a rep for being VERY stable.
Also if you update your SF licenses to 8.8 r14 first, the Nikon 4000 demo might then work. After all it will likely put stuff into those shared folders, which is why you may not have been able to access your other versions.
As a total aside. My Nikon 9000 quit working yesterday giving Nikon FS errors. I talked to Kitten in a panic and asked if a Tech Support person was available and that I was willing to pay for same. She said Mr. Boris was on a call and would have him get to me when finished. In the mean time, she sent me the TeamViewer app, asked what the code #'s where so Boris you check into my situation. He took over my screen shortly later, scooped up some log files, had me open the Epson scanner, etc. and looked at a lot of stuff. Said he would send the info to Germany and call me about 9am next day. This morning I had an email, support ticket from the the Director of Support, Testing master, name Sonke Noack from Germany. He asked me to check into some things, etc. Turns out that when I changed out the old firewire cable and the thunderbolt adaptor to a different old firewire cable everything was working again.
My point here is that I have always been very impressed with LSI and how they treat there customers.