Streaming music throughout the house on a budget?

Without trying to deny you the fun of trying to get some network broadcast solution up and running, there is always the option of just buying a FM transmitter and listen with normal radios (no need to synchronize anything). A benefit is that you do not need any wiring, handy for bathrooms etc. There is one downside though, the audio quality will not be excellent.

Update: FM frequency planning:

Some of the FM transmitters only supports a very limited number (typically 3) of fixed frequencies to send on. Make sure that if you buy such one that it matches the available spectrum in your environment. Otherwise you probably want one where you can select your own frequency from a continuous range.

As a help to map the available frequencies, I wrote a script a couple of years ago to plot FM radio station frequencies along an axis from 87MHz to 108MHz, using the names of each radio station as vertical labels using gnuplot.

Don't know about controlling it with your iphone but you could set up your own shoutcast server.

It's basically an internet radio station on your own network. Set up any computer in the house and connect to it and you're done.

I think it'd be easier to run audio cables then get separate PCs to sync up exactly.

On the software front, many media players have plugins that let you control them over HTTP. This would let you control the player/playlist with your iPhone, assuming you're connected using WiFi.

I like foobar2000, though it's not entirely open source. foohttpserver plugin lets you control it over the web.

Alternatively, Winamp has multiple plugins for a web interface, but winamp is a bit bloated these days.

I don't really know about Linux, but I'd imagine there are analogs there.

While you wouldn't be able to do the iPhone control thing natively with this software alone, you can get pretty good low-latency streaming using VLC & it's Multicast features. Admittedly it's a little finicky to setup, but it's worked well for me for some similar setups. Lots of trial and error.

Just put VLC on all your computers and on whichever one that has your host-library, set it up to either play the music from a playlist or grab it from the line-in. If your host happens to be a mac, you can use SoundFlower to snag the output.

To get the iPhone control working, @Fake Name's answer does mention software tends to have HTTP control these days. I'm sure you could find a decent music player that does, then just use VLC in the live/line-in configuration to snag the audio from that computer.