My recommendation is that you update your A/V Amplifier. 

When SONOS AMP is configured for surround, Line-In and the Subwoofer connections (wired and wireless) are disabled. A front channel AMP supports L/R only with a high level output for a powered subwoofer. You could use a SONOS SUB (or two). 

No, you cannot strap additional front speakers onto a SONOS soundbar. The max for an ARC based system is ARC + two surrounds + two SUB’s.

Yet another chat bot post, covering what has already been said. 
 

Edit: Hmmm, the offending post seems to have disappeared ;)

And providing bad advice too: “You'll need at least one Sonos speaker for the center channel and two Sonos speakers (either two identical Sonos speakers or one pair) for the left and right channels.” There’s no center speaker in Sonos. It’s either a soundbar or the “phantom center” an Amp computes.

Thanks for this insight. This phantom center speaker sounds to me like a complete dead loss.

I am thinking of sticking to a conventional set up as suggested by Buzz.

As I’ve mentioned before, since Sonos released this ‘phantom center channel’ solution, I don’t recall a single person complaining about it. I take from that data point that it works well. 

However, I have not tried it myself. 

I was in your same situation but add in bad hearing. I just wasn’t willing to risk the phantom center and went with an Arc. I’ve been less than happy with the Arc as a solution as there is no control to make the center channel louder than the L/R or surrounds. The speech enhancement option does help though.

We love what the new Sonos brought us in simplicity and ease of use but for many TV shows we really miss our old AVR where it was simple to crank the center channel up so we could hear and understand the dialog.

We and others have long-standing requests for a Center volume control setting.

Thanks for all this feedback. Reading this I am also of the view either not to use Sonos for home theatre, or to go for a Soundbar to give a physical centre channel. 

A decent AV amp is not much different cost-wise to the cost of two Sonos Amps and it is not clear if my existing third-party sub will work nicely with this set up so another Sonos cost.

The Arc seems to do well for most folks with the center channel as is, I’d really put it at the top of my list, adding a Sub or mini-Sub and then surrounds unless you have un-correctable hearing loss.

The ease of use of Sonos and the variety of musical sources it supports makes it far easier to use than an AVR type setup.

Just to clear up any misconceptions regarding the “Phantom Center Channel”….

If you have ever listened to a vocal recording through two properly placed speakers (L/R) and were seated at the mid-point of the two speakers approximately 6-8 ft away the vocals should have appeared to come straight at you. That is because the vocals were mixed to project from the left and right speakers. Other instruments or back-up vocals may have been mixed to the left or right to add positional depth. 

When viewing  a movie (either via disc or stream) if a dedicated center speaker is not detected by the receiving device (i.e Sonos Amp or AV receiver) the material that was recorded for a center channel speaker is sent to both left and right speakers to create the “Phantom Center” channel. 

So as far as sound is concerned the audio mixed for the center channel is not a “complete dead loss” (and can be enjoyed) even though the dynamics may not be as pronounced as when there is a dedicated center channel speaker.

Since most cannot do an A/B comparison (dedicated center channel vs phamton center channel) the detail loss by not having a dedicated center channel is moot. In short “you can’t miss what you can’t measure”. 

AJTek - thanks for your comment

• If you have ever listened to a vocal recording through two properly placed speakers (L/R) and were seated at the mid-point of the two speakers approximately 6-8 ft away the vocals should have appeared to come straight at you. That is because the vocals were mixed to project from the left and right speakers. Other instruments or back-up vocals may have been mixed to the left or right to add positional depth. 

I tend to disagree. Sorry. The reason is that when I am in “the listening chair” for stereo what you say about the soundstage makes perfect sense, with speakers ‘toed in’ etc, etc. I don’t doubt that it can work perfectly in a world with a single viewer, watching a movie in the same way we may listen to music.  

For me, at least, this generally does not apply to home theatre situations. There are more likely to be a bunch of people sitting and lounging in the viewing/listening space, in different positions, mostly not in the single perfect position.

Admittedly, I haven’t tried it (and have no plans to do so) but it seems to me that there is no-chance that the virtual central channel works properly in my real-world home theatre listening scenario above.

Given I don’t want a soundbar, I have already made plans for a conventional 5.1 system, making use of my existing speakers, a new AV Amp and using a Sonos Port (or BlueSound Node )

I’d really lean towards the Port.

If it will work in your room I’d also plan on Atmos playback at some point. Maybe not add the speakers yet but make sure the AVR will support it.

Atmos and Port compatible: 

https://www.crutchfield.com/g_10420/Home-Theater-Receivers.html?fa=1&o=v#&nvpair=FFNumber_Of_Channels|nrank0007]7&nvpair=FFNumber_Of_Channels|nrank0009]9&nvpair=AG_Surround%20Sound%20Formats|YCDolby_Atmos&nvpair=AG_General_Features|FFSonos_Integration

Stanley_4. I am 100% going the same way you suggest but will test the Arc first before settling on pure Sonos or Sonos port with AV Amp.

I don’t like the sound of the AMP as Home Theatre solution (pun intended) and the information that once the AMP is configured in home theatre mode the sub won’t work for music is the final nail in the coffin (assuming I have understood the comments above correctly).

The front AMP will support a subwoofer and Line-In, a surround AMP will not support subwoofer or Line-In.

Thanks Buzz. The more I hear, the more I realise that Sonos is best for music, unless you get into the soundbar set up when it is excellent. Totally understandable but not sure if we want a soundbar in our set up. The Playbase appealed back in the day but that is now old news.