You can get sound from your stereo system to some other place in the house using one of a few alternatives to wired audio networks. Many of these systems are more useful for a point-to-point connection - getting audio from one specific room to another - than for connecting every room.
Line-level audio signals can be successfully carried over Category 5e (CAT-5e) cables in your walls using systems from a variety of manufacturers. These systems range from inexpensive systems that convert the left and right line-level outputs of an audio device into a balanced signal to full-fledged, expensive audio (and video!) distribution systems that provide true multizone audio over CAT-5e.
Many of the companies that sell CAT-5e audio systems use proprietary technologies. So it's best to stick to one brand. Don't try to mix and match, because the audio system may not work.
Balanced cable systems
A balun is named for its function in a network - it converts a signal back and forth from balanced cable systems (such as CAT-5e cables) and unbalanced cable systems (such as audio RCA cables). A balanced line-level signal is capable of going a long distance - up to 1000 feet. A balun is a small passive device (meaning it doesn't need any external power) about the size of a deck of cards, with receptacles on both sides (an RJ-45 on one side, and two or more RCA jacks on the other).
Baluns are deployed in pairs, so you're not going to build a whole-home audio network with them. They fit into your network when you want to get audio from one place to another (a "point-to-point" network).
One balun is associated with the source device (such as a CD player or the Audio Out ports of a receiver), and connects, through an RCA patch cable, to the left and right Audio Out channels. This balun is then plugged into the CAT-5e cable using a CAT-5e patch cable. At the other end of the network, the process is reversed. The second balun plugs into the RJ-45 outlet on your wall (again using a patch cable), and then plugs into the left and right Audio In jacks of the remote amplifier or receiver that you're feeding the signal to.
You can't just plug the output of the remote balun into a pair of speakers and expect music. There is one exception to this: If you have powered loudspeakers (that is, with built-in amplifiers), you don't need an intermediate amp or receiver.
Audio baluns use one pair of the conductors in a CAT-5e cable for each of the left and right stereo audio channels. Typical CAT-5e cables have eight conductors - so you have four left. Some balun manufacturers build baluns that use these four extra wires to carry composite or S-video signals, so you can carry audio and video over the same CAT-5e. This is a great solution if you just need to share a source device such as a DVD player in one remote location - because DVD players also play CDs, you can carry video, audio, or both easily and cheaply using a couple of spare lengths of CAT-5e in your walls.
Single-zone CAT-5e audio-distribution systems
The next step up in the world of audio over CAT-5e moves beyond the point-to-point limitation of baluns and provides a single-zone audio-distribution network to multiple locations throughout the home. These systems typically use custom faceplates that replace standard RJ-45 faceplates in each room. These faceplates have a pair of female RCA audio jacks that can connect to any standard audio source device or amplifier/receiver.
In the room containing the source device you want to share throughout the home, you simply plug a stereo audio patch cable between the device and the faceplate. In remote rooms, you use an audio patch cable to connect the faceplate to the inputs of a local receiver or amplifier. Connecting these remote outlets is a special CAT-5e audio hub located in your wiring closet. This hub takes the source signal and distributes it to every other CAT-5e outlet connected to the hub.
Most of these systems are designed to connect to only one source device - they typically can't switch between different source devices. If you can afford it, and you have more than one audio source you want to share with the rest of your house, invest in a multizone, multisource system. In most cases, the faceplates for single and multizone systems are identical, so - as long as you don't switch brands in midstream - you should be able to start with a single-zone system and upgrade to a multizone, multisource system when your budget permits.
These systems often don't use all eight conductors in a CAT-5e cable to carry audio. Many systems take advantage of this by carrying other signals, such as IR signals for your remote-control system, so you don't need to install a separate IR network.
Multizone CAT-5e audio-distribution systems
If you want the utmost in flexibility and capability in a CAT-5e-based audio-distribution system, you need a system that can carry different audio programs to different parts of the house simultaneously - a multizone, multisource system. CAT-5e systems are the top-of-the-line, best-you-can-buy solution, but they can be expensive.
In terms of network architecture, these systems are laid out in a fashion similar to single-zone audio systems. Custom wall outlets and faceplates connect to the CAT-5e in your walls and provide connections to and from audio (and in some cases, video) systems throughout the home. A hub system in your wiring closet ties everything together.
