I have created an extension to SimpleAudioEngine that is opensource and free to use if anyone is interested. If the mods approve I will submit a link to it. I want nothing in return for it just looking to help out the community as it has helped me.
The basics of what it can do that SimpleAudioEngine cannot is built in toggle for mute/unmute (with an option to fade in/out), fade in/out background music to whatever level you want (and take as little or as much time as you want to perform the fade) and it also has the ability to save whatever volume levels you decide you want for your game i.e. if you want the background music to be at 0.5 and sound effects at 0.75 you do it once and then it saves those values and uses them everytime the game is opened (there is also a function built in so you can change the default values).