The music will probably improve because you added a second One.  Just make sure you set the “Music Playback” setting to Full not Ambient.  It’s in Settings - Room name for Arc/Ones - Surround Audio.

 Don’t aim the One surrounds directly at you.  You don’t want direct sound from them.  Experiment with them turned away from you.  My best surround setup was with dipole ( wired out of phase ) speakers mounted on the side walls above my seated position.  Because they were wired out of phase internally you never really heard any sound from them that gave away their position, but you knew they were contributing to the sound stage.

That would be a good setup and the kitchen sound should be decent for music if you set the Full Mode. You could also just rotate the 100s 180 degrees when switching between movies and TV watching.

I’d be tempted to put an additional 100 in the kitchen too.

Since you already own a One, use that for music and point it to or place it in the kitchen (maybe group it with the Beam and surrounds). No need to rearrange the speakers.

Move the ONE to the far end of the kitchen counter. When playing music the ONE can be Grouped with the TV Room. Set the surround Room for full and don’t attempt to Group the Kitchen ONE while watching TV.

I agree that adding a second ONE for the kitchen would improve the kitchen listening experience by offering proper stereo, however, I don’t see a good location for this second ONE in your diagram. Where do you spend most of your time when listening to music in the kitchen? Would it be possible to place a pair of ONE’s symmetrical to that listening position?

I agree with placing two Era 100’s behind the couch. No where does Sonos mention “angling” the speakers inward to the seating/listening area as necessary. However, you can experiment. I have Era 300’s and Era 100’s as surrounds mounted on stands and neither are angled. 

Placing the Sonos One in the kitchen and Grouping it to your Arc Ultra is a good idea for Music.

I’d not Group it for TV audio as there is a 75ms delay; thus creating an echo effect. 

Thanks a lot everyone for your replies!

I’ll make sure to use the Full mode for music, that’s a great tip I didn’t know about.

I thought I had read somewhere that the rear speakers should be angled this way, but if it’s not strictly necessary, I’ll try different orientations and see how they work both in the TV area and in the kitchen.

As for the One, I wasn’t planning on keeping it, as I was thinking of selling it to help fund the new setup. My goal is to keep things simple, avoid having to group and ungroup speakers constantly, and ideally, have the setup work seamlessly for both music and TV.

With just the One right now, I rarely go over 30% since the room isn’t that big (about 250 sq ft for the kitchen + living room). Replacing it with the Arc Ultra and two Era 100s already feels like a big jump, so adding another speaker just for the kitchen feels overkill to me. What do you think?

Thanks again for all the great advice so far, it’s really helping me think things through!

Ultimately, it’s you and your ears that need to be happy.