This 2nd port works with a regular TV receiver, probably with a touner - and if you put 18V on that port, that port will switch polarisation for the wideband transponder and the CMO port remains the same.
The 2nd port obviously will only work if the CMO transverter is switched on since the 25 MHz reference comes from there.
I put an adapter F->BNC on the CMO-modified port to prevent me plugging in a normal tuner on that port - the 13/18V on the modified port would instantly kill the LNB.
And the 2nd port is rock stable as well since it uses the same reference - connecting a SDR receiver only measures the drift of the SDR dongle, and connecting a TV receiver I was able to receive Palestine TV which is on one of the transponders on BADR4 which is is on the same position.
It switches polarisation with 13/18V and switches LO, for that port only, if 22kHz is sent, as is common with "universal LNB's".
I can even use this modified twin LNB with a POTY.
My personal favorite with this is the Megasat Diavolo Twin. Very good reception this way.
73 de HB9RYZ