AAC is the "best" BT codec currently supported by Apple, and is far better than basic SBC BT from an iOS device. I generally don't stream anything from my iPhone, but on the odd occasion, and with IEMs (not an HD800!) I'll have a casual listen, and would much prefer having the best available codec for that purpose. If you read up on AAC, you'll know that, given an AAC BT link, information from the iPhone doesn't have to be resampled (up or down) during transmission, which preserves a semblance of quality, and gives you at least the equivalent of 320kbps 'transparency'. It's a minor 'issue', like I said, but there's no reason for FiiO not to include support for AAC in the M11 when it does so with all of its other non-DAP BT hardware, and other manufacturers include it as standard.