what is my system

It seems some refer to the Arc HT bonded setup as 5.1.2

That’s Front left/centre/right & Rear left/right plus the .LFE (Sub) channel plus 2 x left/right (Atmos) height channels

Others refer to it as 7.1 where (presumably) the two height channels are just included amongst the Front/Rear channels. The .1 being the .LFE (Sub) Channel.

Just to confuse a little… the .1 (.LFE) Sub channel can actually have two Sonos Subs attached to it.😀

At least that’s my own understanding of things,

I guess one might also arguably infer that there are perhaps two ‘pseudo’ (left/right) side audio channels in an Arc/Era/Sub HT mix, thus making it a 7.1.2 setup. See the image that I have added to below.🤷‍♂️ (…it’s not within my own personal thinking however).

i got an answer from someone that saying my current system is 9.2.4.   I don’t understand why so many different answer.

again,  (one Arc), (two Subs), (two Era 300 surround).

Need a expert to answer this question please.

thank you very much!

In reality, the old x.y.z listing of discrete channels is a moot point.  Atmos is a positional codec, so there are no discrete channels.  With Atmos, a sound is mapped to a room, and what is coming from the rears in my room may be coming from the side firing Arc speakers in someone else’s room.  So the listing of channels means nothing. 

The exact meaning and relevance of x.y.z has mutated a bit over the years. Here is a discussion of surround sound history.

And honestly, I’m curious as to why this is so important to you. Pick one, go with it. As long as the system sounds good to you, you’re fine.