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Question: Can 2 of these units be run at the same time in the same room?  Would the transmitters interfere with each other?
Document: I purchased the Soundcast wireless system to avoid running rear speaker wire under carpet and heavy furniture. I had reservations that it would work in part because the units were small and concern other wireless devices would interfere with the signal. Nevertheless with the confidence of Amazon's return policy I ordered it. The install was fairly easy after reading the directions. Do that. Don't just assume you "can figure it out." there is an order of making the connections that is necessary. As other reviewers have indicated the term "wireless" applies to getting the audio signal from the transmitter ( near TV or A/V amplifier) to a pair of remote speakers.
I have had this wireless system in my living room for a few weeks now. They work beautifully. The sound that I get through my Bose bookshelf speakers is good. No audio artifacts, just good clear sound. And best of all, I don't have to run any wires across my living room. :-)  So far, I am quite satisfied with this wireless system.ADDENDUM:  It's been a little over two years now (May, 2013) and I still really like these units. I do notice, however, that sometimes, there will be a mysterious and loud "pop" sound coming from the surround speakers (which are Bose 161's) when the units are running.
This is a great wireless transmitter if you do not want to run wires across the room, for whatever reasons.Pros:1. Very simple to setup. It comes with two wires for left and right connections from HT Receiver to the Soundcast transmitter. Just hook up the wires and power, and you're good to go.2. The transmitter uses negligible power. The receiver uses more, as it has to output to speakers, but it goes on standby on inactivity. So that saves power.3. Volume level is pre-set and works perfectly out-of-box.
I was not sure what to expect from this unit but it far surpassed my expectations both for ease in set up and for sound quality. Our slab concrete base with hardwood flooring would have made it difficult to run traditional rear surround speaker wiring. This system allowed us to hook up the rear speakers without any fuss and the small size of the sending and receiving units made them easy to hide. Highly recommend.
The Soundcast transmitter interfered with its Wifi. The Roku was still able to connect to my network but its speed was terrible. I moved the Soundcast transmitter further away at about 5ft and I no longer have any problems. Some observations... the transmitter looks for an unused 2.4ghz channel every time it is turned on. If you turn other devices on after the transmitter, Roku for example, both could be working on the same channel. Apple TV can handle 5ghz.I love it and would buy it again.
I have purchased 3 of these systems and all work great. I use one in the house for my rear surround speakers and 2 are hooked up to a receiver in the house and power Klipsch rock speakers in the backyard. The outdoor receivers took a little bit of time to position so they received the signal (I buried them in a small rubbermaid container so they are weatherproofed and hidden) once I got a clear signal I have not had a problem and the speakers are louder and clearer than the neighbors would prefer.
We purchased these, because we had no wire to run the wires from our sound system to the rear speakers without having to step on them. My husband set the receiver about 10 feet away from the amplifier and had no complaints. Pretty much a plug and play thing. We haven't noticed any lag on the sound and our sound system still sounds amazing. We even have our wireless router in the same room, about 6 feet away, and there's no interference. We would recommend them to anyone who is needing something to make their speakers wireless.
My living room is hard wood floor and there is no way to run wires from the TV back to the couch or you would walk across them getting to the kitchen or front door or stairs. I have an ONKYO TX-SR608 Receiver by the way for all of the people saying it won't work with Audyssey (however it's spelled), IT DOES. When I first plugged it in there was a slight slight delay in the rear speakers. The sound was just barely behind the front speakers but most people wouldn't notice it.
Unlike most other reviewers, I ordered these to use with my front speakers. I have an oddly shaped living room that forced me to get creative with my setup. I was at a loss on how to run surround sound in this living room since there was literally nowhere for me to hide the wires. I decided to try these out to see how they would work with my front speakers, since getting speaker wire to my back speakers was a non-issue for my setup. Much to my satisfaction, it ended up being a great solution.1.
This was very easy to get up and running. I am using for one rear speaker (def tech pro monitor 800)with my pioneer vsx-60. The way my living room is set up, I can discretely run a wire for the rear left speaker behind a couch but it would have been impossible to wire to the right side of the room (hard wood floors, fire place, door way to another room and a wet bar were all obstacles to getting the rear right to the desired position).This worked right away and synced perfectly with the automatic calibration that pioneer receiver has for speaker placement and volume (mcacc).I also looked at the rocket fish wireless system.
Answer: I would say each set comes with a pair and it is "paired". So there is probably no interference. And then I found this review and confirmed that there should have no interference. So let's try it.http://www.practical-home-theater-guide.com/soundcast-wireless-system.html