The "Y" is combining the L/R into a mono signal, and splitting the mono at the TV top lay both L&R info from each of the TV speakers. You can use 2 coax cables with RCA connectors on each end to build your own cables,

 

This will give you 2ch Mono signal, which is an unwanted downgrade. Use 2 coax cables with male RCA connectors and you won't need the other adapters at all.

 

I have to use the single coax. I have a centralized av system/rack in the house with 4 coax cables running to each tv in the house. Three of the coax cables are used for component video. That leaves one coax for the audio signal - thus the y adapters. I don't know why who ever prewired the house did it this way. :/

 

This will give you 2ch Mono signal, which is an unwanted downgrade. Use 2 coax cables with male RCA connectors and you won't need the other adapters at all.

I have to use coax for audio. I have a centralized av rack/closet. Four coax cables run to each tv in the house. Three are used for component video and the fourth is for audio. I have no idea why the pre-wire guys would have done it this way. I can't get a stereo audio signal to my TVs. Unless I'm missing something......

 

The only way to get stereo is to use the SPDIF out if you have it. However this is limited to 10 metres.

See: http://en.wikipedia.org/wiki/S/PDIF

 

Another option would be a stereo RF modulator. Here is one that I found; they work just like the old RF outputs on VCRs.

The S/PDIF out IS a better option if you can use it; they make Toslink (optical digital) to Coaxial digital converters if all you have is Toslink. I checked Parts Express and found this and this. They probably have something to convert stereo RCA to digital coaxial, too!

 

I cant' run any new cables to the TV. The DirectTV box is in a closet on the first floor and all the wiring terminates there. Fromt that closet the wiring goes thru the house up to the to TVs in the house. There is no way to add any more in-wall wiring.

 

None of these options require running new wire in the walls. I'd guess that the Direct TV box already has an RF out that you could use to run audio/video upstairs. On the back of the Direct TV box there should be a threaded connection with "channel 3" (or 4) under it. That is a RF output; you could connect the coaxial cable to that output and simply connect that same cable to the TV located in the room that the cable ends. My only caution is that the RF out is probably mono.

You could add a stereo RF converter as stated in an earlier post; the converter should NOT require running any other wires in the house. I found several on Amazon; here is one. For <$10 you have a solution that requires NO new wires in the walls!

 

Isn't the RF signal on the back of the DirectTV box Standard definition (i.e. not high def?)

 

Yes, it's standard def. Based on the description on the wiring, I can not think of a way to get a HD pic to the other TVs. IF there are 3 coaxial cables that run to the same room, a component video signal would work. If there are 4, the Toslink out could be converted to S/PDIF coaxial digital, too.

 

What model TV? If it has digital audio in, use that over coax (SPDIF, orange RCA connector on DTV box). I've successfully run it much farther than 30M on RG6. If it doesn't, you're stuck with either some sort of modulator or digital encoder-/decoder set.
Most speakers on flat screens these days are pretty weak, and often on the back of the TV. I wouldn't worry about using mono audio at the TV myself, the quality difference out of typical tv speakers will be barely noticeable, and it's by far the cheapest option.
Another option would be modulating the component+audio output of the directv box. This would require some slightly costly hardware though, and component video is old tech, and being phased out. You're better off investing the money in a set of HDMI over coax extenders (assuming a HDMI enabled tv), which will give you full digital HD plus audio over one or more (more is usually much cheaper) coax's. Hopefully you have good RG6 wire (quad shielded even better) in place, not RG59.

If it's not a HDMI TV, just use the RF (threaded coax F connector) output over a single coax and call it a day. Unless somehow you have a rare CRT HD TV with component and no HDMI or DVI, or an early commercial flat panel or something.