I definitely think you're onto something, and suspect you'll be happy with the 4 little Yamahas based on others' reports on the swarm approach. You may find, however, that the corners give you more room gain than you want (I did). I highly recommend the "subwoofer crawl"--putting the first sub in the listening position and finding the best bass response, placing the 1st sub there, etc. then optimizing the DSP for each sub with REW. I found that by changing crossover frequency, damping factor, and volume I could significantly flatten the bass response and I just have 2 subs (still planning on adding at least one more, this time a 15", or maybe a Yamaha based on your results
). I think it was Geddes that suggests best results with different sub sizes, damping factors, etc. to help randomize thus flatten the modes.