The SM400TSN unit does not have PIP (Picture In Picture) function. You can only use HDMI (or any other source) as a whole screen. You need to set your Background to Source and then choose HDMI. Then save the template with a name or your preference and then schedule it through the Magicinfo pro server/scheduler. I use this on my MXN screens.
From what I have learnt, the DXN series (apart from the 52") have the Genesis Video Scaller, and the rest have the MStar scaler. Geneis can do PIP and MStar does not.
The latest CXN-2 product is a Genesis video scaller and that's why you can do PIP, but in the CXN (just like the TSN) it has a MStar scaler and you cannot do PIP.
Bill