Using ZP120 as a 'dumb' amp. Its input from a Port (gen2/S2)

I have several Sonos ZP120 circa 2006.  Is it possible to set them up to be a dumb amp? My thought would be to use a newer Sonos PORT RCA outpout that would feed into the ZP120.   Im cool with setting the ZP120’s up using the S1 app, but then simply Set-it and forget it and uninstall the app.   
what I dont know, and looking for advise from the comminuty, is;
-  Can the ZP120, if never touched fall back and stay at the Line-in input setting?

- Is the Sonos PORT RCA output varabile? ie: If the ZP120 volume is permenatly set to say, 90%, would the varabile RCA outbout from the PORT be akin to a volume control. There by adjusting the room volume from the S2 app?

- does the ZP120 have a sleep, and//or auto wake from the RCA input.  id hate to add to the global warming by having them amplfy hiss and dead air. ;-) 

ive got 2 Listening Zones with 2 and 4 in-celing speakers respectvily. The zone with 4 speakers cannot handel the power of a newer Sonos AMP @ 4 Oms ( I think).  I use the zones vary rarely so the Idea of dropping $1400 (or $1000 and burning two 30% discount codes) + new celing speakers stings a bit too much to the wallet.  repurposing the ZP120’s and spending $500 on a Port is eaiser for me.  If this configuration is not possible or to “jankey” then for the $500+/- price point Ill look at getting a Roam2 or ERA100 and/or Beam Gen2 and/or sub mini. Then simply abandoning the in-celing speakers. *insert sad face* 

for details the 4 x  in-celing speakers are  super old Klipsh 2-way CS-650-R 35watt (140 wattt peak) 8Ohm 

thanks for any advice. 
cheers,
chad