The confirmation came in the form a reply from a Google developer to a question put up by a user on the company's Issue Tracker website.
Here's what the developer said: "Unfortunately, aptX and aptX HD are not supported on Nexus 6p and Nexus 5X - only on newer devices."
For those who aren't aware, aptX is a proprietary streaming protocol currently owned by Qualcomm. In layman's terms, it is aimed at providing better audio over Bluetooth. In fact, Qualcomm claims aptX audio enables "CD-like quality" wireless audio.