Method 1: USB Update (Recommended for Reliability)

Because Onkyo’s network servers are sometimes offline for legacy devices, USB is the safest method for the 2021 update. txnr646 firmware update 2021

Onkyo TX-NR646 Firmware Update 2021: Stability, Chromecast, and HDMI 2.0 Fixes

Introduction

For owners of the Onkyo TX-NR646, 2021 represented a critical year for device maintenance. While the 7.2-channel THX-certified receiver had long been discontinued (succeeded by the NR676 and later models), Onkyo continued to push firmware updates to address lingering bugs, particularly those related to network streaming stability and HDCP 2.2 handshake issues with newer 4K streaming devices. For those still using the Onkyo TX-NR646 Go

The most significant update for the Onkyo TX-NR646 in the modern era arrived on December 2, 2020 While the 7

The 2021 firmware update was specifically engineered to resolve these legacy pains. It is widely considered the "end-of-life" stable patch—meaning if your receiver is still on a 2019 or earlier build, you are missing critical stability fixes.