Raspberry Pi Multicast TV server is really good to be capture and save by the Slice with MythTV addon or other addon as PVR.
This is a nice idea.(I really mean that)
Solutions are available though, which will not require that excessive hardware zoo.
combine this... https://digitaldevices.de/produkte/dvb-komponenten/max-s8/or this... https://digitaldevices.de/produkte/dvb-komponenten/max-a8/or even both at the same time with some ITX board and... http://tvheadend.org/and you're good to go.(I'm using this setup with older DD cards.)
Or go the integrated way... https://digitaldevices.de/produkte/netzwerk-tv-tuner/octopus-net-a8/ and use http://tvheadend.org/ over IPTV / DVB/IP.(I didn't test this (yet).)
(NO, I'm not working for Digital Devices .)
Thanks you for your information to make a better solution !