Boxes that have a second video encoder can support PiP.
In order to check if box has a second video encoder you can check using the following command from telnet.
# ls -1 /dev/dvb/adapter0/video* /dev/dvb/adapter0/video0 /dev/dvb/adapter0/video1
If the output contains /dev/dvb/adapter0/video1 then PiP supported.
Please note that some boxes support only SD channels in PiP, more information about PiP in supported boxes can be found in Settop Box Comparison