It’s unclear why the handsets aren’t supported, but we can only assume it’s because aptX requires a crucial piece of hardware that they’re missing — something developers are unable to create a workaround to deal with.
For those who missed its announcement, aptX is an innovative wireless streaming protocol owned by Qualcomm, which supposedly provides CD-like audio quality over Bluetooth.
Android O is said to be one of Android’s beefiest updates to date, bringing a number of new features to the operating system, including picture-in-picture, notification dots and application badges.
Article source: https://www.technobuffalo.com/2017/07/14/nexus-5x-nexus-6p-aptx-bluetooth-support/