In the manual it says:

eARC LINK Diva can extract up to Atmos HBR over TrueHD from capable eARC TV connected at TX0 and output it via AUDIO OUT to feed any AVR input capable of decoding such format.

So that might be the answer.  But at 399 Euros ($432.76), you are almost in new TV territory.  Plus, it doesn’t seem to be available in the US, except for over $500 on EBay.

I contacted HDFury a few days ago to get on print if any of their products can push back audio over eARC to a soundbar with HDMI eARC. The answer was no, no product to this date will be able to do this. The Diva, as well as vertex and maestro, are able to extract audio from your TVs eARC HDMI port but they are all built to output the audio signal as regular HDMI signal, and the Arc does not support that kind of signal.

Is that still the case? Can I not use an Diva instead of an Arcana?

No, I don’t think you can.  As @egrunden says, the Arc requires an eARC signal (or HDMI-ARC), not an HDMI signal, and only the Arcana produces that.

So why does it says all over the Diva product page that it does support eARC?

https://www.hdfury.eu/shop/hdfurydiva/

I was hoping the Diva and Vertex2 provide the same functionality as the Arcana. It sure looks like there is not reason they should not be able to do so at the hardware level so a firmware upgrade should be able to enable that right?

As I wrote 5 months ago, the eARC feature of the HDFury products (except Arcana) is simply being able to receive the return audio from the tv connected at the output and push it forward to the hdmi output going to a receiver. The Arcana is still the only product able to actually produce a eARC signal that the Sonos Arc can read and play. You see, there’s a huge difference between reading eARC from the tv and actually produce an eARC signal for the Sonos Arc. It’s not just about extracting the audio and sending it on different pins, all the equipment needs to make “handshakes” with each other and the standard is typically built to just accept one handshake between a tv with eARC and the single output at the soundbar. And yes, as eARC is a return channel the audio input at the soundbar is actually, technically, an hdmi output. So, to get this working HDFury made some exceptional engineering with the Arcana which makes the soundbar think it’s a tv and the tv think it’s a soundbar and the input think it’s a tv mixed up of both. To make this there is custom hardware, and that can’t be put in the vertex or the diva by software update. For certain they’ll update the products with this functionality at some point but as of today you’ll need the arcana. You can of course combine it with a diva or a vertex, but you’ll need the arcana to sit between the Sonos arc and any of them to get any audio out of the Sonos arc.

Wrong, I believe.  ‘Support’ does not mean ‘output’.  Diva is for people with eArc TVs and soundbars /AVRS that don’t support eARC.

I bought the Arcana because I don’t have eARC on my TV (or even the ability to play Atmos over DD+) but I do have an eARC-compatible soundbar (the Sonos Arc).

It has done exactly what I wanted. 

Very odd, I guess I’ll just have to wait for a device that combines both Diva and Arcana features.

You can use both in the same setup. I’m using Vertex and Arcana without any issue, fully supported by HD Fury, as is using Diva and Arcana together.  Heck, they even sell a package of Diva+Arcana $100 off the price of both separately.

https://www.hdfury.com/product/4k-arcana-18gbps/

Under the Quantity option, you can select this package.  If you look under the ‘Getting Started’ tab, they have diagrams of you how can connect your devices, Diva/Vertex, Arana and TV...although you can also set it up like ‘Multi sources’ as well.

HDFury has stated that they do intend to that their next generation of product likely will have Arcana functionality built in, however they estimate that’s 2-3 years off.  They have other development tasks that are taking priority right now.

So what’s the use of the ARC output on Vertex and Diva if it not compatible with ARC devices?

I guess I’ll just wait until they add that feature to Diva.

It’s not an ARC output per se, it’s an HDMI input with ARC.  That port will send normal video and audio to your TV and receive ARC audio.  Why would it need to receive ARC audio?  Because, if you’re using a TV’s smart apps, that’s the only way your Diva/Vertex can receive the audio, and then pass on to sound system (one that receives audio through normal HDMI rather than ARC).

Perhaps looking at it a different way, the port on Diva/Vertex that is label as ARC has the same functionality as the port on the Sonos Arc...it receives ARC audio from a TV.  It is not like the ARC port on your TV, which sends out ARC audio.   Arcana on the other hand, does have a port that sends out ARC audio, just like your TV.

This feature isn’t going to be added to Diva.  It is promised to be in a Diva 2 product in 2-3 years. And the  price for Diva 2 could very well be more expensive than getting Diva and Arcana separately right now.

You seem to have decided that Diva is the answer, but you don’t know what the question is.  I haven’t a clue what problem you are trying to solve.  Have you?

I was told Diva alone won’t work and I trust you guys. Now I’m just being curious about what it does.
I was just considering switching from optical to HDMI and trying to understand what it takes.

I have four source devices plugged to my TV HDMI and an s/pdif optical switch that was feeding a Playbar until I replaced it by a Sonos Arc last month. Passive 3D Philips TV from 2015 is only used as a monitor really, I’m not even using its optical output.

Actually there is a fifth source device, Fire TV plugged to Oppo UDP HDMI input.

Well on the Diva product page it says 4 HDMI In, 3 HDMI Out and one of the HDMI output is labelled ARC so that’s rather confusing.

yes, ARC is rather confusing in general.  Your TV HDMI input that is labeled output is actually sending audio out.  Sonos decided not to label there port at all to avoid the confusion.

A ‘trick’ I use to help me keep it straight is that ARC is like a raspberry bertet...it goes in through the out door (out door).

lame joke, yes, and possibly too obscure, but works for me.