There is a slider to increase/reduce the surrounds’ volume relative to the front channels. 
Or contact Sonos support to check for a faulty Arc Ultra - you might have a faulty unit. 

I don’t think it’s faulty, but I will say the app is terrible. I went to add a voice assistant and instead of adding it, it stopped recognizing one speaker and I had to factory reset every speaker in my surround system. Super buggy.

And yes, I could change the slider but that defeat the purpose of Trueplay, which is dialing in the perfect audio.

“And yes, I could change the slider but that defeat the purpose of Trueplay, which is dialing in the perfect audio.”
 

Tries to, at least, but doesn’t always get it right. 

I have got the same impression. Arc ultra, upgraded from an Arc, 2 Era 300 as Surrounds and a 4Gen and 3Gen Sub, upgraded from a 3Gen and 2Gen.

Left the settings as they are, true play measured twice in advanced mode. The surround speakers are very present and loud in this configuration while the bass at the same time is absolutely underwhelming. I cranked up the sub level to +2 and the Equalizer Bass setting to +1 but still I am missing the spine and stomach shaking whoomp below 120hz that I got used to from my 2G and 3G sub.

I love how the Arc ultra plays in every direction with almost pinpoint accuracy. That is pretty much the same feeling I had when the Arc replaced my Playbar. The surround speakers may be toned down a bit, but I really am missing bass. Especially since the 4G Sub is marketed as double the bass of a 3G or something along those lines.

Adjusting the EQ and Surround Audio levels after performing Trueplay doesn’t “defeat the purpose”. It allows you to tweak the settings to fit your specific room environment and audio preferences. If your surrounds are overpowering the Ultra, lower the Surround Audio levels. It’s as simple as that.

There is definitely something off with how the Ultra interacts with the 300s for me, the volume of the surrounds is way too loud. And this is coming from someone that enjoys exaggerating surround levels usually.

The Nintendo Switch has a good simple test where it plays tones on 5 channels. With the regular Arc, all 5 tones sound like the same volume right after Trueplay. With the Ultra, the surround sounds are extremely louder than the front. It’s not subtle in the slightest, I have to set the surround levels to -9 to get them to sound similar.

I’m assuming there’s something specific about our setup that is causing this, because I can’t imagine this would be either intentional or untested by Sonos engineers.

Ok so for me is other problems i have fives at rear and ultra at front all connects as surround but my fives are closer than ultra and seems that i would like tk increase the sound just of ultra but instead i have slider where reduces sound of fives and ultra why theres no options to increase on ultra sound instead of decreasing fives as i dont need less sound i need more but to adjust ultra you cant at all not everyone has 10meters on 10 meters rooms and not everyone putting sofas in the middle of the room if you turn of true play you can adjust fives the distance is it possible to connect them all without having surround lets say just to have full potential from the speakers ? 

First of all, this is one long run on sentence.  Very difficult to read, never mind decipher what you are saying.  Punctuation and capitalization would help. 

Second of all, the output is relative, not definitive. Think about it:  The Arc can only perform at the level it can perform, you can’t make it magically “louder” by sliding a slider, it’s overall output at level “X” is fixed.  You can only reduce the relative volume of the surrounds, which is why they only give an adjustment to the surrounds. Similarly, raising the relative volume of the surrounds is not going to affect the overall output of the Arc, only the volume of the surrounds in relation to the volume of the Arc.

Thirdly, most consider Sonos Fives to be overkill for surrounds.  Their performance and fidelity are wasted doing surrounds duty.