I was trying to find a solution for this problem for some time and finally I have found one. It uses mix of virtual interfaces, which not all of them are free, but they are also not very expensive either.
What you need is Dante Via software (49.95 USD) and VB-CABLE Virtual Audio Devices A+B & C+D (min. 10 EUR). Both of those applications are very versatile, worth their price. You’ll need also ASIO4ALL driver, that will route audio in Reaper.
Dante doesn’t need any introduction. VB-Audio is Vincent Burel – creator of many interesting audio plugins and software tools. He is also known for creating VS3 plugins for Pyramix. I am using extensively his Voicemeeter Potato.
Install software, ASIO4ALL, Dante Via and VB-CABLE instances. You’ll need three VB-CABLE interfaces, each one gives you 8 channels, and you will need 19 of them.
Enabel Dante on Zylia ZM-1 ASIO driver.
Add Zylia ZM-1 to Audio Destinantions in Dante Via.
Route 19 channels of Zylia ZM-1 to VB-CABLE devices channels (8+8+3).
In Reaper set ASIO4ALL as your ASIO driver. Configure your ASIO4ALL driver so that you have VB-CABLE a, B and C set as inputs.
Then set your preferred output device as output only.
Set track with input from the VB-Audio CABLE, and on MASTER track set output device. On the recording track you can set up Zylia Ambisonic Plugin and binauralizer plugin of your choice.
Here you have working Zylia ZM-1 binaural monitoring on Windows 10.
There is a drawback. This method produces significant latency, but if you are monitoring from a control room or some distance with closed headphones this shouldn’t be an issue.
You can also use this for setting up the session, and than record without direct monitoring.