I haven't looked at faxing things from windows in a long while, but what is the "Fax" thing I see already existing in the Windows printer drivers?

https://faxauthority.com/windows-8-fax/

So yeah, based on that, it looks like Windows 8+ comes with a built-in fax printer driver.

Whether or not your VOIP line is compatible with faxes would be something you should be able to look up. Faxes operate at low speed with pretty old technology, so I could envision a world where VOIP lines, at least some of them, should be able to handle faxes. Indeed, this page seems to think it might work if you configure it to slow down the transmission rate:

https://www.voipmechanic.com/faxingissuesandotherdevices.htm

This page says that you can fax over VOIP as long as your VOIP service and your fax device support something called "T38":

https://www.3cx.com/pbx/t38/

Oh hey, I just looked up Ooma directly and they seem to say that they do support faxing over an Ooma line, so that looks like it should be expected to work:

http://support.ooma.com/home/faxing-with-ooma

So I think that you should be OK if you just have a faxmodem of some kind. If you've got a serial port working on your windows PC that works well enough to communicate with the Empeg Car serial port, then it should work for any old faxmodem if you have an old one gathering dust in storage somewhere. Surely you've got a USRobotics modem buried in a box somewhere, back from the olden days? :-)

If not, I think it sounds like it'd be worth it to find some kind of USB fax modem and give it a try.