I had a similar problem with my Onkyo amp which only has HDMI 2.2 inputs. My solution has been to plug in a cheap HDMI 1.3 splitter like this one: eBay HDMI splitter 2 Output 1 Input 2 Way Switch
HDMI cable in from T4000, another one out from port 1 to the AV amp. Problem solved as it negotiates with the HDMI splitter which has a HDMI 1.3 port rather than the 2.2 on the amp. Doesn't even seem to need an external power supply.
Make sure you get one which actually takes one input and splits it to two displays (even though you only use one). Many of them take two input sources and feed them to one display. Also make sure you don't get a 4k compatible one or you're back where you started.
Seems I'm not allowed to post a direct link to the device. Here's a picture of the type I've used, the power supply doesn't seem to be required in my case.
I have the same splitter, and this is what I used in 2016, since then I have connected straight to the TV and used ARC, which works perfectly.
But, now there is some Atmos content i want to access that.
So i am back trying again with the splitter, does is pass through Atmos?
It's a ball ache for me to get to all the cables to try it just to be dissappointed.