Somewhere in a previous post on this subject, I described the details of how a buddy with cable, and three (?) Dish receivers merged it all together.
He found a sweet deal on a low-pass filter that I think rolled off around channel 80.
I believe they're in the $30..50 range, but he found some for $10 on eBay.
Brand... Microcircuits?
He then set two or three agile-modulators to 83, 85, & 87 (?)
They were a close-out at Radio Shack for around $25.
Sadoun appears to sell a similar unit, and at least on eBay, offers
two or more at significantly reduced prices.
I'm uncertain as to the ability of either to manage stereo audio, but that's something you can look into.
Then, he took the incoming cable through the filter, along with the output of all the modulators, and put them into the outputs of a standard resistive 4:1 splitter.
The normal "input" was now the output, with all signals combined.
He lucked out, as all the signal levels were good enough to feed his house wiring.
The filter prevented the modulators from going out onto the cable, and it also kept any cable crap on his modulator frequencies (chan 80-90) from interfering with his own transmissions.
More info on this lashup, and an ex-TV engineer with a more exotic house system can be found under my name, in the last 18 months, in the FTA section.