in simpler words, NO it can't be done, cuz the bandwidth on the modem for ptcl is limited to a few mb/s. streaming video on one channel takes ~2mb/s, so even if you had the hardware to stream multiple channels, it's not possible due to low bandwidth.
On the other hand, cable works on satellite signals...Satellites transmit signals which receivers pick up. The cable operators have dozens of boxes (some have bought ptcl boxes by the dozens as well).
Interesting comparison with ptcl-like service vs the cable, the ptcl gives you one channel at a time only, where as the cable carries ALL the channels in it at the same time. So the cable has a lot of bandwidth. So in terms of amount of data being provided to you, the cable gives you maybe 10 times as much data or even more. It's only we watch one channel at a time, though newer TVs have that option of watching multiple channels on the screen.
So basically, to answer your question, you need two boxes and I guess they would be on two separate lines. or you can get the much cheaper cable and put a splitter on it and use as many TVs with it as you want.