Compile Flags:
There are some #defines you can set to change the behavior at compile time. Most you shouldn't touch.
The one worth noting is ENABLE_ALMIXER_THREADS. If enabled, ALmixer_Update() is automatically called on a background thread so you no longer have to explicitly call it. (The function turns into a no-op so your existing code won't break.)
Having Update run in a separate thread has some advantages, particularly for streaming audio as all the OpenAL buffer queuing happens in this function. It is less likely the background thread will be blocked for long periods and thus less likely your buffer queues will be starved. However, this means you need to be extra careful about what you do in callback functions as they are invoked from the background thread. I still consider this feature a experimental (though I am starting to use it more myself) and there may still be bugs.
Building:
This project uses CMake.
Check out CMake at http://www.cmake.org
Check out my screencast tutorial at: http://playcontrol.net/ewing/screencasts/getting_started_with_cmake_.html
Typical commandline: (from inside the ALmixer directory)
mkdir BUILD
cd BUILD
cmake ..
make
Or use the ccmake or the CMake GUI to make it easier to configure options like ENABLE_ALMIXER_THREADS.