It turned out, these ports couldn't actually live up to their promise of passing through 8K signals or 4K/120Hz graphics from the (then new) Xbox Series X game console.

Fortunately Denon and Marantz owner Sound United responded quickly and positively to discovering the problem, promising to find a solution for everyone who bought one of the affected 2020 AVRs. Now that solution has finally arrived in the unmissable shape of the SPK618 external HDMI adapter.

The SPK618 sits between the Series X console and the HDMI 2.1 port of affected AV Receivers, converting the signal from the console into something that the AVRs can pass through to compatible TVs and projectors.

When the problem was discovered last October, it was surmised then that the solution would have to come through hardware rather than software, and so it has proved. 

While it might have been tidier aesthetically to have replaced the relevant HDMI boards inside the affected AVRs, such an 'invasive' solution was likely never going to be realistically achievable given that it would have either required engineers to visit customer's homes during a pandemic, or consumers to send their AVRs off to have the upgrade fitted.

Making the addition of an external HDMI adapter to your kit much easier to live with is that Sound United is making it available free of charge. All you need to do is register your interest in receiving the adapter before your eligible AVR's warranty expires. Claims can be made from May 15 2021, with SPK618s set to start shipping from the end of May.

Do note, though, that you only need to bother ordering the SPK618 adapter if you have both an Xbox Series X console and a display capable of handling 4K/120Hz feeds.

Sound United models affected by the HDMI bug are as follows: Denon AVR-A110, Denon AVR-X6700H, Denon AVR-X4700H, Denon AVR-X3700H, Denon AVR-X2700H, Denon AVR-S960H, Marantz AV7706, Marantz SR8015, Marantz SR7015, Marantz SR6015, Marantz SR5015, and Marantz NR1711.

In the US, UK, France, Germany and The Netherlands, anyone wanting to take advantage of the SPK618 upgrade will need to take the following steps:

1. Go to www.denon.com/hdmiadapter for Denon, or go to www.marantz.com/hdmiadapter for Marantz.
2. Fill out the form with the required information.
3. Once they've received their SPK618, users will need to update their AVR's firmware to complete the process.

In other countries, including the Asia Pacific region, rather than following the steps above, you should contact your local dealer/distributor about receiving the adapter and then again make sure your AVR is updated with the latest firmware once your adapter arrives. 

The entire upgrade process has been designed to be easy enough for anyone to achieve. Still, Sound United has gone to the trouble of putting together a YouTube video you can refer to if you find yourself struggling.

While it would have been better if the Denon and Marantz AVR HDMI issues had never happened, it's actually quite impressive to see a brand willing to go as far as Sound United has to fix a highly technical issue that would have been almost impossible to test for ahead of the Xbox Series X's launch.