If you want to access your iTunes library in a different room to your computer, simply plug in an Airport Express, then plug in a speaker. There are a huge array of possibilities available at all price points. Mine is the Braven 625s.
Once this is done, you can use Remote to control iTunes.
The AirPlay indicator (bottom right) gives you control over the volume. Other control function in pretty much the same fashion as the stock Music app.

Once this is done, you can use Remote to control iTunes.

The AirPlay indicator (bottom right) gives you control over the volume. Other control function in pretty much the same fashion as the stock Music app.