Thanks guys for the answers.
Yes, I would like an x86 machine.
Speaking of usb3, I need them to backup the internal hard disk to external storage.
I would use a ssd (no more than 128 / 256GB, depends on the price) and a sata internal hdd 2/4TB.
About the dvb-t2 device, I'm oriented to huppage win HD quad. I know a dvb-t2 tuner can record multiple channels on the same mux, but I prefer to be quiet enough for simultaneous use (wife and children). But i have a doubt here, will this tuner support 4k?
About dvb-s2x tuner i don't have any idea on what to go. Myabe dual s2x tuner would be enough anyway.
Yes @Paraic McDonagh, you're right, spend a lot on tuners and have a limited system would be a shame.
Speaking of transconding, as I said, it would be really rare, i never had the needed until today, just i would not exclud it. But i could easily avoid occasional transcoding if that would mean spend double respect without it.
EDIT:
i'm looking for j5005 pentium fanless solution, it should have hw transconding that for 1 one stream transcoding would be enough. What do you think? A user here
https://tvheadend.org/d/5646-tvheadend-transcode-and-hw-minimum?r=31462#message-31462 is able to do 4 transcoding HD using j4205 igpu.
The problem anyway would be the pci-e limited to only one.