I want to use s-video and those seem to require expensive powered devices for splitting.
I was also recently looking for an inexpensive S-video Y cable to run two S-video devices off of one output. I came up with two options.
This from RadioShack, which is marked as an extender but can be used as a splitter as well (look closely at the backside of the plugs). The second option is
this from MCM, which is the option I went with. The short bit of cable between the connectors is thinner than I would like, but it does the job.
Be aware that splitting an output like that will halve the impedance, and halve the voltage that each input sees. The obvious effect will be that the picture will be significantly dimmer than before. You will need to recalibrate to match the new levels. Same applies to splitting composite or audio cables (6dB reduction in volume for audio).
You'd need one of those more expensive distribution amplifiers to avoid that. Say something like
this would fit the bill nicely, but is overkill and overly expensive. You may be able to find cheaper elsewhere.
If you're handy with a soldering iron you should be able to construct a simple s-video distribution amp. All you need is some connectors, a board, a power source, and a two good op-amps configured for 6dB gain. Add some buffers to the output if you feel like it. Probably cost around $20 in parts (off the top of my head, so don't hold me to that).
For the life of me I can't understand why Dish doesn't put two S-Video outputs in their boxes. On something like the 311 I can sort of understand it, but on a high-end device like the 921 (and 721 before it), it's almost insulting to not have at least two. And for higher-end devices like the 721 and 522 there should be component outputs. The signal is sent in component video (all MPEG2 video is), so then recombining the Cb and Cr channels for S-Video output is just silly, especially since even non-HD televisions have component inputs standard these days. [steps off soapbox]
-- Dave
