I have a much smaller house, my home network is a (much) smaller subset of what you are running. It is a star shaped network, all cabling end up in the tech.cupboard so it’s easy to rewire into all kinds of topologies. All CAT6 and gigabit switches as well. I use RJ45 plugs mounted next to the power sockets in floor level, if I could redo it, I would also go for at least two RJ45s / powersocket, only have single plugs now and you run out of them much faster than you think.
My house has three floors, and the bottom one is partially below ground level and has a massive concrete roof – I must have a separate WLAN access point here to get coverage. No problems really, but worth a thought when planning a new network.
Audio is streamed over the Wifi network using Apple Airport Express and AirTunes. The main speaker system is very minimalized – two active Genelec speakers (no external amplifier!) and one Airport Express, nothing more. All music is streamed wirelessly from any computer in the house, either using iTunes or AirFoil. This also makes it possible to play music synchronized sets of several speakers on different floors if you want the same music wherever you go in the house – perfect for parties. Volume is controlled from the playing computer at all times. Only a powerswitch for the main speaker system, nothing more. Very kidproof too – have not had any problems at all so far. The whole music archive is digitalized since at least 10 years back – CDs are so 80’s.