@Fun4ever This should be straight forward operation as long as the IP address is a private IP address. I can see that your AX55 FW release is pretty old one. You can update the FW to the latest one...

@Taste66 This is the only public data that can be seen for technical parameters of the switches. I'm using few of these and never had any issue with multicast traffic.

@Fun4ever You have to change the LAN IP address of the router first (router will restart itself) and then set its DHCP server pool.

@Fun4ever A DHCP pool should be in the range of 172.16.10.2 - 172.16.10.254. Can you post a screenshot of the DHCP settings and error message.

@Taste66 You can see the SG-105 performance parameters in its data sheet - here.

@Fun4ever As long as you set a 24 bit mask (255.255.255.0) this should work as expected.