More I research, the more I think I should just buy some Yamaha DBR12's one at a time until I have ten of them in the barn.
Yamaha DBR12 Powered Speaker | Musician's Friend (musiciansfriend.com)
You can look at something like that, but for that money you can pick up a used 12 channel amplifier on eBay which will give you 60 watts per channel for clean power to up to 24 speakers (2 per channel). Many amps can have their outputs bridged to provide even higher power per speaker if you want to add another amp in the future. More importantly, these are designed from the start with the idea that a dozen speakers will be connected to them at a time. These amps are big, well built, and heavy. This is what pros use in these types of setups to get a lot of audio, at good levels, everywhere in a space.
More importantly, on your budget, you may find some models which do exactly what you want at a reasonable price from the start. You can pick up the proper amp, then just put in as many speakers as your budget allows. But, when you want more speakers, you can get them knowing the amplifier can handle it.
I have bought a dozen or more amps off of eBay for running a lot of speakers and MOST have performed great right out of the box. Only a couple had to be returned (not at my expense!) because they didn't work as advertised.
The two on this list I really like are the Sonance 1250. That amp weighs about 80 pounds. It's crazy good. I'm not sure if the condition of the amp encourages me, but it may be perfect for your setup. Also, the SpeakerCraft model is very good and SpeakerCraft has a long reputation of quality products. They were used a ton in installs over the years, and there is a lot of their stuff on eBay at a great price. These amps were all well over $1,000 when new.
Examples...
Here we have the impressive AV1260 from B&K. This unit is in very clean condition and functions great. Features: 12 channels providing 55 WPC at 8Ω or 85 WPC at 4Ω. Each channel can be assigned Left, Right or Mono.
www.ebay.com
You are buying a Sonance SONAMP 1250 MKII 12 Channel Power Amplifier. WHAT YOU SEE IS WHAT YOU GET.
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Find many great new & used options and get the best deals for SpeakerCraft BB1235 12 Channel Power Amplifier at the best online prices at eBay! Free shipping for many products!
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If you could swing a bit more, the higher power amps cost a bit more, but may be worth it. NOTE! The SpeakerCraft 1235 models allow for you to bridge channels. So, a 12 channel amp with 35 watts per channel, becomes a 6 channel amp with 60 or 70 watts per channel. Adding a second amp with 12 total speakers effectively doubles the amount of power to those speakers. Also, if you want to have more speakers, they are stable with 4 ohm loads, capable of driving up to 24 speakers per amplifier!
More than $400 shipped to your door, but under $600 with 50+ watts per channel and in good condition (yes, I am scouring eBay for you here)...
Model: Niles Audio SI-1260. Type : Power Integration Amplifier. Color : Black.
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Find many great new & used options and get the best deals for SpeakerCraft Big Bang BB1265 12 Channel Power Amplifier/ Amp - YOU SHIP it at the best online prices at eBay! Free shipping for many products!
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Sonance SONAMP | 1250 MKII Power Amp | Includes Power Cord | ■S■ TESTED ■S■.
www.ebay.com
For speakers, I would put a bunch of 8" 3-way speakers into MDF back boxes which you make yourself out of the materials you have available. Then build the subwoofers separately, in the future, for when you want things to really rock. Put some speakers like this into the back boxes you build and mount, and you will have amazing sound in the space with 6 pairs...
In-wall speakers allow you to expand your listening environment throughout your entire home, as well as removing the clutter of giant box speakers, giving you back your living sp
www.monoprice.com
Total cost: About $1,000. You would need some speaker wire for all of it as well.