To clarify Joseph’s remarks on AAC, we don’t support the format due to licensing constraints imposed on us by having our own decoder. That said, for iOS in particular (and Android) we are able to decode AAC using platform provided decoders, for iOS that decoder is the AudioQueue API. AudioQueue is what is imposing the constraint, I tested your file in the debugger and I can see an “unsupported format error” being returned, however I get no such error with 6 channel or stereo.
If you have control over the encoding side of things, I highly recommend using our FSB format, we have command line tools and an API that you can use to integrate it with your pipeline (no FMOD Studio required). You can create individual files (one FSB per source sound) or pack multiple files into one. The formats it supports are our recommendations and their decoding is the most optimized.
If that’s not an option for you and memory / performance aren’t a major concern I’d recommend using Ogg Vorbis, it’s a solid format and quite flexible. At this stage we have no plans for a fully cross-platform Opus decoder, we will be supporting it within our FSB container format for consoles with hardware decoders only.