That is correct. The Sub Mini cannot be used as a 2nd Sub.

Dual Sub setups are only possible with the Sub, not Sub Mini.

Before you return the Sub Mini, you might like to do an experiment.  Remove the One SLs as surround speakers and set them up as a stereo pair and add the Sub Mini.  See how that sounds for music.  You may like it enough to buy a couple more One SLs rather than return the Sub Mini.  Or you may not. 

Hmm, love it @John B! I will check this out! Thanks so much

I'd be very nterested to hear what you think.

@John B I bought the mini to bump bass at my desk while listening to music from my home theater set up; as my office sits off my living room where the home theater is set up... in one large room. Per your suggestion, I’ve set up the SLs and Mini as a second stereo system at my desk.

I like it very much and am considering going with two systems now in adding a second pair of SLs. Great idea; never would have occured to me. Sonos should give you a cut of the $700-ish extra spend, lol. 

I was thinking in terms of buying a second Gen3 for this part of the room, but felt that would blow out the neighbors. For a similar spend, your idea of a second stereo system is much more sonic value for the dosh!

Thanks so much.

Thanks for posting back. Excellent though the Sonos soundbars are, I have never been totally convinced about them (or any other soundbar) for music. I have a pair of Play;1s and I have always thought the sound was excellent given the size and price of the speakers. The Sub Mini should fill out the sound nicely.

I'm glad to have helped. 

@jnelly   There is probably no significance in your choice of the word 'system' for the proposed new speakers. But just to make sure, I shall point out that you must add the new speakers to your existing system

You should end up with two 'rooms' within a single system.

Appreciate the concern and input @John B  - indeed I have two Sonos Rooms set up in the “Sonos System”, and was using the “system” designation as I think of my home theater as 1 system, and now the desktop as a second system. (I’m 57)

It was super easy to set everything up within the two rooms, Trueplay it etc. (still like TruePlay off, since 14.10 or when ever the sound architecture was re-engineered by Sonos), In essence (including stands) I now have a $900 desktop system/room, LOL. May be a bit of overkill; we’ll see...

As far as Soundbars...John. I didn’t even know what OLED (had a Panny Plasma) Atmos, eArc, Dolby digital, 5.1.2 etc. was in Oct. 2021 when I bought my Arc. I hadn’t upgraded any A/V equipment in 10+ years.  A year later I’ve got two new Oleds, two Sonos systems/rooms, and a Samsung soundbar.

Been through a lot of equipment and have returned a lot of equipment in settling on the above.

At the end of the day, soundbars are a space and convenience trade-off.

The Arc “5.1.2” 

• Wireless, with a soundbar for the front channels was the only home theater form factor for me
• Quotes above are because Atmos up-firing drivers are 90% hype, once in while, depending on the creator’s mix, I get some height, and/or object based audio objects happening in my 3 dimensional sound environ., lol (for real Atmos I highly suggest ceiling housed, down-firing speakers).
• Overall this Room/system sounds great; I mean was really amazed at Sonos out of the box and I can very “audiophile” picky… (Bose 900 and Samsung were good, too)
• Ability to tailor the sound through all the S2 app eq variables is great
• The versatility of the Arc system through the S2 app is great - for music and home theater
• Ease of set up and use is great
• And, I’ve paid for this convenience ($2100-ish, but that is fine by me based on value)
• Only real competitor last Oct. was the Sony AT-A9 w/sub and a top of the line Samsung which I could not EQ from my couch.

Samsung Q700B Soundbar “3.1.2”

• I wanted to add some bass to my bedroom TV
• Based on a price of $349 at Costco, phenomenal value
  • I would not pay the $5 or $699 regular price
  • Tried a  Sonos Ray, honestly, it sounded terrible
• The Q700B bar also has a lot of eq variables
• And, I have way more bass than I need
• I can AirPlay to it as a Roon endpoint
• Super easy to set up and use, both from Samsung’s remote and it’s App.

Hope this is informative on Soundbars from a more old school, purist, who actually knows what decent sound sounds like, but isn’t willing to get involved in the audiophile world, as the sonic upside isn’t worth the time or dosh - for me. Sonos is plenty satisfying sonically.

EDIT - I’ve been listening to my new One SL Pair / Sub mini system/room at my desk for the last 2 hours or so, my first sit since putting it together on your suggestion from yesterday- it sounds great!

EDIT 2 - Comparing the music listening experience, between

• Arc “5.1.2”, ($2,048: Arc, Pair One SLs, Sub3; no Costco items), and
• One SLs 2.1 ($798: Sub mini, Pair One SLs/with Costco pricing )

I’d pay the extra $1,250for the Arc “5.1.2” system.

• There is processing going in the Arc that makes the overall listening experience better; I’m thinking of the Arc as the “receiver”...
• The Sub 3 kills the Mini for articulation on the low end (though this could also be in combo with the Arc)
• I like listening to stereo music in the “5.1.2” format

@John B