Another thing to consider regarding your layout considerations is going to an under-mounted tub. I was looking at 60 inch tubs to get a little more decking space and ended up going with a 72 inch tub that when it is under-mounted will give me about the same deck space as the 60 as there is 5 inches of flange all the way around the 72" tub (10 inches off of left to right and front to back, rectangular tub). I get the interior space of the big tub with the footprint of the smaller one. I will also say a little prayer to my favorite wrench to send a master plumber your way. All of us DIYers need all the help we can get.

I'm not a tech or an audiophile, just a homeowner who has been hooking up and installing stereo equipment for lots of years. First, it would be nice to see how the speakers sound. If you can get your receiver to work long enough, you could connect the receiver's speaker outputs to the inputs in your office, one set at a time, and see if you like the way the speakers sound in the respective rooms, how the volume controls work, etc. If I understand you, there are two sets of inputs in your office. Most standard stereo receivers (not necessarily AV receivers) will allow you to hook up two sets of speakers and switch them on and off independently. Or maybe you could borrow a receiver to test. I don't think I'd put much money into fixing the old receiver, as much as you may love it. I went that route, and decided to buy a more modern, inexpensive Aiwa receiver. It's fine for my purposes and even has a remote control, which you don't get with the older ones (will only work in the same room however). If you need to hook up more than two sets of speakers, then you will need a more sophisticated solution. But it's great that you've got speakers and wiring installed. Just some thoughts.

Speakers outside good, amplifier outside bad.... Amp has to be out of the elements, either under cover or inside. I run an Apple Mac Mini computer through a Denon A/V receiver, which is connected to speakers throughout our home as well as outside in the pool area. I can play my entire iTunes library or access my Sirius Internet Radio off the Mac Mini. All the speakers have their own volume controls located throughout the house and outside at the bar, cabana and hot tub. We power 5 pairs of speakers around the pool. 2 rock speakers, 2 inground, 2 "PipeAudio" speakers in the cabana, and 2 Bose 301's at the bar and 2 marine waterproof speakers located in the planter pedestals that surround the raised pool spa. I can control the Mac Mini from another laptop that sits in the cabana and is connected to my wireless computer network. I use logmein.com to do that. It's just like gotomypc.com, except it's free. This allows us to choose channels on the Sirius Internet Radio, and control what plays out of iTunes, never leaving the cabana. W Sounds complicated, but it's really not. I did all the hookups myself. Here's some photos.

Not sure on the exact equivalent of CSA (Canadian Standards Association) FT-4 but I believe it is CL2 or CL3 - riser rated. Basically, what it comes down to is that if a fire was to start at or near the in-wall cable, would the cable contribute to the fire spreading? With the correct insulation, as in in-wall rated, it would not substantially contribute. Between floors, in vertical walls, it should be riser rated. If the cable passes through air handling areas (very unlikely in residential) it must be plenum rated as well which means the fumes emitted are within specific toxic limits. The silver/gold zip-cord type of speaker wire is hardly ever in-wall rated... but the good thing is that the proper in-wall speaker cable (CL2/CL3) is usually cheaper. Coax, Video, Audio, Ethernet cables all must be in-wall rated as well.