I forgot to add that a pair of 1 PI speakers per channel will play very loud. All you do is build four of the 1Pi speakers, and stack them inverted with the tweeters close to each other. They will play LOUD. Not to say the 1Pi won't. My son inherited my 1Pi speakers, and with a sub shakes his townhouse. I believe he uses Quicksilver Minis, that's only twenty five tube watts a channel.
Enjoy your project.