Is there a secure way to access the receiver remotely over the Internet?

[Morini]

Do you install OPNsense on the E2 boxes, or on your servers, or on the router, or on some combination of these?

Dan

OPNsense takes on the role of (replaces) your router, but it can be a lot more besides. It will run on just about any old pc for the purposes of trying it out (providing it has more than one network interface). You can even run it a vm, I did that myself for a while and whilst it worked perfectly fine there are too many disadvantages running routers virtualised. Dedicated hardware is better in the long run.

If you have any old PC hardware lying around then that is the quickest and easiest way forward. There are small multi NIC mini PC's available very cheaply on aliexpress or ebay and these make great opnsense boxes. I won't post links because I don't think it is allowed.

As pointed out you could also consider accessing your E2 boxes via a VPN. Opnsense supports both openVPN and wireguard, so setting that up is quite easy should you decide to take that path.