Well I reply to myself with some news:
I opened a ticket to Digital Devices about two problems:
1) SNR and Signal Strength columns are empty with OctopusNET S2 device
2) A lot of Uncorrected/Transport/Continuity Errors on the four tuners
They assumed the first problem that will be resolved with next firmware (no Idea when)
but
they returned me to tvheadend staff for point number 2.
Before opening an issue, I'll ask again:
Nobody else using an OctopusNET S2/4 device with tvheadend?
Thanks
Gigius