I thought the line-in was disabled when the 100’s or 300’s are used as surrounds. What is your setup and how is the turntable connected? 

Sorry - I think I have it: Era 300’s as surrounds, 100’s as a second room and tt connected to a 100? 
 

You then group the two rooms, to both play the tt source.

You should still get full range audio from that setup, and full EQ control over Arc/Sub/300’s room. 
 

You could try different configs: separate Sub from Arc and connect to the 100’s for example. If still little bass, check delay and level settings on the 100 line-in, or I’d question stylus and preamp setups. 

Yep, your second comment is the way it is set up.  With grouping the two rooms you mean this? The only way I can see in the app that makes is possible.

ill see about the preamp. I think that might be what’s causing it.

Have you tried adjusting the Line-In Source Level?

Yes, that’s grouping. 
 

Is it the Sonos linein adaptor? Most other makes are not suitable. 
 

Try the tt into the other 100. Remove the 300’s as surrounds and try input to them. 

Yes it’s the line in adaptor from Sonos.

just tried the line in on the 300’s. Already a lot better, but still not great because I want the 300s for my surround system for tv as well.

would the Sonos Port be the solution?

seems as though feeding the vinyl through the 100 and then grouping it, the audio is limited because of the 100. Then grouping it doesn’t deepen the music because it’s coming from the limited 100s.

What do you guys think?

have tried adjusting the line in as well but little change

Addition. Will the 300’s play vinyl as well when I use the Port, or will they not seeing as they are connnected to the surround set?

As ​@Mr. T suggested, you can also adjust the linein level. 
 

When speakers are set up as surrounds they will only play with the soundbar playing too. You can agjust volume to surrounds for audio but the soundbar will still play. 

There should be no difference between using the Line-In on the Era 100 compared to the Era 300, other than the acoustics of the respective speakers.

When used as surrounds, the main front driver of the Era 300 is disabled, so they will not sound the same as when they are used as a stereo pair.

In the Arc Ultra’s room settings, under Surround Audio have you selected “Full” for Music Playback?

You can also increase the Music Level slider.

Thanks both! Found the right line in adapter page in the app. Turns out it was set at level 2. Putting it higher is already better, will try this for some time to see what it does.

thanks again.

After enjoying for a while, try the 300’s as your music speakers and the 100’s as surrounds and see which configuration you prefer. Swap in the Sub too! Then get your wallet out…

Good idea. We have the 300’s set up with wall mounts around the couch so I think we’ll keep it this way though.

A pair of 300s and a Sub is amazing playing Atmos content, I really notice when Amazon doesn't have a track in Atmos and drops back to stereo. You might reconfigure your room to play with that setup and consider the 300s if adding Sonos to another room

So adjusting the Line-In Source Level as I previously suggested was the “fix”.