@selje For the most part, I followed these instructions here:

https://starreveld.com/PVS6%20Access%20and%20API.pdf

Rather than putting an rPi system in the box, though, I just ran the Ethernet cable to a system I had with both wireless and wired interfaces; the WiFi sits on the home net, while the wired interface does DHCP to get an address from the SunPower box, then polls it to get the data out.

Once that was set up, getting it into Home Assistant was mostly a matter of installing the integration. Figuring out which power signals belonged to which panel took a while; if you don't have it yet, use the SunPower app to make a map of the serial number for each panel and its location.

I'm debating whether to stick with this system, or to take up Enphase on its offer and swap out the SunPower box entirely. The Enphase monitor would be a supported product, and it seemingly has much better Home Assistant support.