Hi

In a Home Theater setup you can only Bond together the Arc, sub (or sub x 2) and Era 300 x 2 as rears. You cannot bond any more speakers to that setup. 

You can add additional speakers for music in the same room such two Sonos Ones. They would NOT be part of the Home theater. 

In my Media Room I have:

• Home Theater: Arc, Sub x 2 and One x 2 as rears (Name: LG)
• Music: Five x 2 in stereo pair with sub (Name: Stereo)
• Vinyl: Sonos Amp with Pro-Ject Debut Carbon Turntable, Sonos Sub and Definitive Book Shelf Speakers (Name: Turntable)

All are physically in the same room. However, each is named differently.

If memory serves...the Max number of speakers/components on one system is 32. Therefore, you could have 32 speakers in one room. However, that would be insane .

The maximum configuration for a surround “Room” is soundbar, two surrounds, and up to two SUB’s, Additional L/R speakers are not supported.

Other speakers can be present in the physical room, but they will be separate Rooms in the SONOS controller. SONOS Rooms can be “Grouped” to play the same music and all Rooms included in the Group will play in sync. Note that there will be a time offset with Rooms Grouped with TV sound. I don’t recommend attempting to add more speakers to the surround Room. If you insist on trying this, you can tinker with the soundbar’s voice sync, but this will usually have a negative impact on lip sync and the Grouped Rooms will not benefit from any surround processing.

Up to 32 units can be part of a SONOS system. A “Bonded” stereo pair of active speakers is a single Room in the SONOS controller, but counts as two units. A surround system is also a single Room, but could be up to five units. If one or more BOOST’s are part of the system, each BOOST counts as a unit, but BOOST’s will not appear as a Room in the controller. 

Up to 32 controllers can be simultaneously active.

FYI, with a little creativity you can identify a Boost as a room (of sorts).

To be clear I have a Asus Mesh Network with three routers connected by Ethernet backhaul. Each Boost is connected to a router (main and two nodes) via Ethernet cable. I have multiple Sonos speakers/Amps/Port on each level. Total Units = 30

Please excuse the “Red Dots” you see in the second image. My system is under construction and units have been sold to upgrade to the Era series. I just need to do some house keeping 

The following is a bit off subject...but it will explain the some of  “Weird” room names you see in the 2nd image.

You’ll note in the second image that the naming convention for my “rooms” is  a bit unorthodox. For instance I have a room listed as “LG” which is a Home Theater located in my Media Room connected to an LG monitor. That room contains other Sonos devices such as Five x 2 in stereo pair with the room name of “Stereo”. 

I can control each via Alexa voice by saying “Alexa..turn on/off LG” or “Alexa..play smooth Jazz on Stereo”. My point being that a “room” does not need to contain the “word” room in the controller.