I live in the UK and I want to share my first experience of returning a defective product. 
My Sub Mini died and following a diagnostic check with a Sonos technician it was agreed the defective unit would be returned for replacement. 
I dropped off the unit to my local UPS collection point yesterday and they, UPS, confirmed it is in their possession. 
The Sonos technician did not mention the destination for the return was Poland or about the option of Advanced Replacement. Consequently I have to wait for the unit to arrive at the Polish site before Sonos will send me the replacement. There is no timeline on when I will receive the replacement. 
The Advanced Replacement option would have accelerated the shipment of the replacement before the the delivery of the defective unit to Poland. 
I have asked Sonos for Advanced Replacement but they say it’s not possible because the defective unit is in transit to Poland. 
We live and learn