Not sure on the sub issue (although more is not always more! - as it seems in this case). 

But on the Apple remote issue - that really should work. Have you tried running the remote control setup again in the app? And also have you got the Arc Ultra connected to the eARC-HDMI port on the TV and got HDMI-CEC (or equivalent, e.g. Anytime+) enabled on the TV?

The Apple Remote is sending information through the Apple TV to your TV set, which then processes the volume commands and sends it via CEC (HDMI-ARC) to the Sonos. The Apple Remote doesn’t connect directly to the Arc, unless you’re connecting via optical, in which case there is no CEC connection.

About a year ago, there were a spate of Apple remotes that needed to be re-serotonin up to connect properly to their Apple TVs. Have you done that process?

I don't think there have been any major changes but I also only have 1 Sub 4. The only thing I think has changed is the dialogue volume but SONOS has also made an update regarding this, I have turned it off completely.

I only use Apple TV and its remote control, I don't even know where my Samsung remote control is.

The first thing you should do is make sure the ATV remote controls are updated as well as your ATV:

How To: Update Remote Firmware On Apple TV - Easy Guide

After that you can do this little trick, it should solve the problem.

4k Apple TV (2025) remote volume disconnected from sound bar

The remote is up to date and control via HDMI CEC works when I: Turn on AppleTV first, let it figure out the CEC stuff with Sonos and switch on the TV afterwards.

Sometimes I have to use “Setup TV” again in the app.

What about Remote Control Setup though? - that is the primary thing to repeat, not Setup TV. 

(Plus also try the ‘trick’ mentioned in a previous post to reconnect the remote.)

Consider the physics of the situation. Subwoofer placement, listener placement, and room size/shape interact.

With respect to the Volume control setting, many users equate the setting to system “power”. If a low number results in “loud”, then the system must be “powerful” and this is good — right? However, the system may be difficult to control at low settings because a one step difference could result in uncomfortable changes in output. Over the years there have been complaints about “difficult to control at low Volume”. SONOS changed the ‘slope’ of the control to expand the options at the low end. This immediately resulted in praise of “easier to operate” and complaints of “less powerful” because some users then needed to operate at higher numbers. The “less powerful” complaints were not justified because ‘100’ still resulted in the same output, but the complainers were very vocal. From version to version SONOS will tinker with the Volume control ‘slope’ and the complaints will flip. It’s a no win situation.

With respect to bass, experiment by disabling one of the SUB’s. While playing a thumping track, walk the room near the walls with a hand-full of PostIt notes. As you discover locations of higher bass, mark the location with a “#1”. You’ll discover a few locations where the bass will seem doubly intense. Add a “!!” to these locations, As you step back, you’ll notice that the notes are more or less regularly spaced around the room. These locations are known as “peaks”. Midway between peaks there are “nulls” where bass is minimized. Placing a subwoofer or listener at a peak will increase bass.

Next, disable SUB #1, enable SUB #2 and repeat the process. The “!!” locations will tend to coincide and the other peaks might move somewhat and the magnitude will be different. This is predictable from the physics, but you are stuck with the physics. A significant detail will be the phase of the SUB’s. If the #1 and #2 peaks coincide, flipping the phase of one SUB will change the magnitude of the peak. This change can be very dramatic. It’s possible that at a given listener and SUB location, adding a second SUB may result in less bass.

You should be able to improve your situation by fussing with phase and location. Trueplay can complicate things by attempting to create a uniform response while the listener wants aggressive bass for movies.