I reckon the receiver option is a good one. I have just done this in our Spanish Villa and I am also running the PRO in my house in UK. Multiroom Audio in Spanish Villa
@nickwild I went with Herdio Speakers as I was short for time. They are not in place yest but only time will tell. The Villa is close to the sea so a harsh environment. “Vamos a ver” as they say in Spanish. We used to have a set of “rocks waterproof speakers” but I wanted to get the speakers off the ground. I am sure the Rocks would not be a good solution on top of the pennines.
Good luck with your waterproof speaker research and let us know how you get on.
Regarding the PRO receiver the sound was probably the best source I have plugged into that arrangement. It provided a really crisp sound, plenty of punch, full range and copped very well with my 24bit 96kHz music collection. However the Rotel Preamp with the Old Skool Bose Speakers has always delivered an incredible sound.
If only Old Skool Bose Speakers were IP66 rated and Pennine Proof 
Regards
Kevin