What model TV do you have? What audio sources have you been testing the system with?

I have a samsung qe55qn95 tv connecting into the arc ultra via eArc.

Sources I've tried so far are the tv streaming apps and music streamed over WiFi to the system from my amazon.music account 

Be sure the TV is set to these settings:

HDMI-eARC Mode: Auto

Digital Output Audio Format: Pass-Through

Also be sure to perform Trueplay tuning and adjust the EQ settings, Height Audio, and Surround Audio levels to your liking.

Try to test the system with Dolby Atmos and 5.1 audio sources.

All set as you suggest apart from the digital output audio format.  I can only select auto or pcm.  I'm in auto.  In pcm it sounds dreadful.

I've tuned trueplay and toggling that doesn't really make a big difference.

Tested several multi channel sources including atmos. I can see the system recognising these formats in the sonos app so that seems to be working OK.  

I think what I'm a buit worried about is that is there an issue with my arc ultra. The suba and era 300s sound great but it's like there is something really missing from the front channels. Especially as I need to use 2/3 volume to get a reasonable output.

I rrealise this is not a particularly scientific comparison but the scale of the q990d that i heard tonight  (without rears hooked up) made me question if I have a a technical problem with my ultra

Make sure Night Sound is NOT enabled and the volume limit is set to 100% in the Sonos app.

Both those settings are as you suggest.

I have the same system as you and if I turn the volume up to the levels you suggest it would be so loud, usually I have I set around 20 and it’s more than loud enough for my room. I performed the basic truplay as full truplay seems to remove all the bass from the subwoofer. I have a Sony tv connected via EARC as opposed to the Samsung but with a digital signal I don’t think the volume level would be effected. Streaming music is slightly quieter bot not to the extent you have mentioned.

Thanks that's very helpful.  I doesn't feel right that I have to have it at 55. 

I mean it's not quiet at 55 but my hearing is ok and this is the level I'm needing to enjoy the system.  20 for movies and music would be very quiet on my system.

Obviously it's not hugely scientific to compare volumes across brands but my friends q990d at 20 makes your ears bleed

I've logged a ticket with support but thanks for your comment. It feels like I have a set up or technical fault on the ultra.

I'd also add that even at 55. There feels like there is a hole in the front soundstage to me.

I had put that down to the fact that I have swapped out a hifi surround sound system with 2 floor standing b&w 804 speakers as my fronts.  So was kind of expecting/accepting some drop in presence fom the soundbar solution

Play something Atmos and listen closely to each speaker to see if it is working.

Can try that but not really sure where the 14 speakers in the bar are.  I wonder would true play tuning flag up is a single driver were not working?

Sonos should be able to see if you call them.

Hmmm seriously considering returning the system

I wouldn’t worry too much about the volume levels on 0-X style volumes being different between brands. Even within the same brand they can be different levels across different products. Some manufacturers have linear 0-100, some don’t because buyers want more control and gradual changes at lower volumes than higher.

If they were -dB volumes then they could be comparable. 

You don’t mention what size your room is vs your friends.

It does feel a little like comparing apples to oranges to strawberries trying to compare the Sonos, Samsung and your B&W based system.

The Sonos and Samsung have a different number of speakers, on board amps, speaker arrangement, power output and sound processing. If you were running the Sonos at near max volume then I’d be concerned.

If the 804 floor standers are the ones I’m thinking of, then they are high end HiFi. If the rest of your surround system is a similar level, then I am not surprised if you find a soundbar is lacking. 24 years ago Nautilus 804 floor standers were ~$3,500 a pair, current 804s make them look like a bargain. You can buy a lot of soundbars for the price of just the 804s nevermind the remaining speakers and surrounds for a full system.

It is possible there is an issue or fault with your Arc and realistically you probably need to wait for support to help identify it from what you have already tried.

Part of me feels compared to what you are used to with the 804s any soundbar based system will sound lacking and very different until you adjust and get used to it. A pair of 804s with suitable separation are likely to have a far better LR + Phantom Centre than any £1,000 sound bar can manage to produce. They are products aimed at very different levels of the consumer market imo.

The sales page and owner’s manual can help you locate the speakers, so can a flashlight held up to the grill.

Give Support a chance, they will do what they can to prevent a return request being made.