I'm sorry that I don't have a good answer for your question. I've got two such machines, both regular ITX motherboards. The main is an Asrock N3700-ITX (only dr

I'm sorry that I don't have a good answer for your question. I've got two such machines, both regular ITX motherboards. The main is an Asrock N3700-ITX (only driving 1080p), the secondary is an ECS KBN-I/2100. The main AP is the "router", which is a Ryzen 5700G on a full ATX board. If I needed another AP, I would get another decently powerful but lower idle current machine to replace the main entertainment center one, and then trickle the N3700 elsewhere. Or if I didn't want to do that, I believe I have seen one or two amd64 boards targeted at being RPi replacements. The biggest thing is I want expansion PCIe so I've got flexibility later. For power supplies, I'm using PicoPSUs on both. But I've also seen motherboards that take 18VDC. Or if you are willing to do some wiring you could power multiple motherboards from one supply.