best way to retrofit after-thought speakers

Depends on how/what was installed. If they just wired a new set of speakers to a Sonos Amp in parallel, it might be hard. Normally, I’d recommend a separate Amp for a new ‘room’, like your hallway, and then you could set the volume for that ‘room’ on its own, using the Sonos controller. Then when you ‘grouped them’, you’d be able to set each room’s volume separately.

Have you gone back to these installers with your concerns?

It’s possible that the new speakers are wired out of phase. A very quick (and not absolutely definitive -- depending somewhat on listening skill and some physical realities) way of investigating this is to swap black and red wires at AMP for one channel. If the issue seems to move to the other area, there is a phase mismatch. Reversing +/- on one speaker in the quieter room will resolve this. It’s a lot more trouble, but the absolute method of investigating phase is to connect a flashlight cell to each speaker. At the instant of connection there will be a “thump” and the woofer cone will jump in or out. The standard is for the cone to jump out at the instant of connection when the {+} terminal of the battery is connected to the {+} terminal of the speaker. All system speakers should jump in the same direction.

Another possibility is that the speakers differ in their efficiency.

Finally, even with proper phase and identical speakers, the room size will vary -- the larger room will always be quieter. In-wall speaker Volume controls for each pair of speakers is the best solution for this.

Thank you for your responses. It feels that because I am sharing the signal the new set of speakers is not getting full signal.

is there a way to amplify the signal to the new speakers? May be use an inline amp? 

Don’t worry about this.

A trick question on a final exam could ask the student to discuss changes in intensity and light color as lamps are added to a circuit or extension cord, but it is so small that the human will not notice. The discussion with respect to speaker output is similar.

Yes, but I don’t recommend this because the added speakers will change Volume along with the originals. Adding a SONOS AMP is easy, and since AMP can connect to the system wirelessly, you could locate it in a nearby closet or on the floor above. You’ll then have independent remote control of both areas. Of course, you’ll need power for the AMP.

Hi Buzz 

thank you for taking the time to reply I will give your suggestion a go 

thanks