I have seven Sonos zone players ("ZPs") scattered throughout my house and they are connected to a wide variety of speakers. Personally, I'd hesitate to spend big $ on monitors for this purpose. The combination of (usually in my case) compressed program material and indifferent internal Sonos amp doesn't invite serious listening.
OTOH, if you use uncompressed files:
I believe that your budget would almost certainly be better put to one of the small non-amplified zone players with signal sensing powered speakers (this will retain the "auto-on" feature of the powered ZP). The only downside here is the extra AC cords for the speakers. An extra benefit is that you can put your current ZP in another location and add any decent, inexpensive monitor for ANOTHER MUSIC ROOM!
I think the little unpowered ZPs are app. $400 and the powered monitors from Quad are available under $1K (from Underwood Audio, among others). I suspect that this kind of combo will be more likely to please than the powered Sonos ZP with just about any $3K monitor. If you're inclined to add a powered (preferably room correcting) sub to this type of set-up, you can actually do something pretty special at your budget - provided that you're using quality program files.
For the most part, I'm not.