Problems setting up printer

I’m working with a client to set up a new Epson ET-3750 printer and am running into an error I cannot find on Epson’s site, or that they recognize.

Computer is a mid-2011 iMac running a clean install of macOS Sierra. Chatting with Epson tech support they say the combination should work fine.

It was behaving poorly/oddly on High Sierra and I did find a Win32 infection on it. Backed up drive with Time Machine, excluding system files, reformatted drive, then did a clean install, taking it back to Sierra. Restored data, ran MWB and Avast and found no infections or malware.

Setup the new printer, attempting first a direct USB connection and then a wireless connection and in both cases when the installation software attempts to Add the printer I get the error message in the image below (server-error-internal-error). When I do the same installation, using the same USB and WiFi setups (including USB cable) on a mid 2014 MacBook Air both work just fine. I can also AirPrint to the printer from iPhones and iPads. It’s just the iMac that will not connect to the printer.

I deleted the Epson folder from Library>Printers, uninstalled all driver software, rebuilt permissions and then started from scratch with a clean download. No change.

Looking for anyone who may have experienced this particular error or have an idea what it relates too.