Hi, unfortunately jriver is like wmc where you would need a tune per channel you are watch so in your description, you will need a min of three tunes cards for what you are trying to achieve, (because jriver dont support,multi mux channels), (ie here in uk all our hd channels are on same mux so in jriver you will need 5 tunner cards min). where other software like mediaportal, nextpvr, (on windows os) support mutli channel mux so if you had a dual card them two can allow you to watch virtual every channel across your pc's so one card can feed all uk hd channels to 5 pc's (ie bbc1 hd , 2, itv hd channel 4 hd etc )
if you just want this setup for live tv with jriver you need lots of cards per channel
hope this has helped