Add this one to the changes or new features that Lumia Denim will bring to entire Lumia Windows Phone 8/ 8.1 range. Seems, with Lumia Denim installed, Lumia owners can enjoy high-quality Bluetooth audio streaming from the phone to supported accessories.
This will be possible because Lumia Denim will enable the aptX audio streaming codec, which makes possible to stream high-quality audio over Bluetooth. One of the FAQ reply by Microsoft support reveals this,
FAQ – Does my Lumia phone support aptX for Bluetooth audio streaming?
Yes, the entire Lumia range with Windows Phone 8 will get an over-the-air update (Lumia Denim) to enable the aptX audio streaming codec.