• SoundEffect API which as the name implies is useful for playing back sound effects with some basic parametric control like looping, volume, pitch, panning (and 3D positioning on Windows and Xbox) etc.
• Media API is useful for playing background music, either a soundtrack with the game content or from your media library.    

As for your current issue though I have a couple more questions if you don't mind - how are you looping the content in XACT? Do you have the loop points defined within the wave file itself or is it something slightly more complicated (e.g.an InteractiveAudio cue with markers etc.)?  

I have read that you can define loop points in a wave file, but I don't have any tool that actually can do it, it seems. My preferred tool is Audacity.

Is there some tool that allows you to set and edit loop points in a wave file that you can recommend? Ideally not a tool that costs hundreds of dollars, as I'm low on that particular resource right now.

Btw: if you try to play two cues with timing done in the application, it will never work quite right. A better way to do it would be to create a playlist in the Sound in XACT, where you have two Play Wave events on two tracks, the second offset by the length of the first. That ought to work fine on PC as well as Xbox.

Audacity's a great editor but I haven't used it since I got SoundForge 9 (which unfortunately costs a lot more). I did a quick search on creating loops in Audacity though and found some sites that explain how to do this.

As for Spin0r's original question the easiest way to solve this is to -

1. Define the loop in a wave editor.
2. Add it to a wave bank.
3. Drag-drop the wave into the sound bank editor to create a cue. This cue should have a sound corresponding to the wave with 1 play wave event on a looping track.
4. Play the cue.

 This should give you accurate looping no matter what platform.

Unfortunately, the markers in Audacity do not get exported to loop points that XACT understands when exporting to WAV. I had already tried that.