This is my proposal for the 3-way layout. The Quad drivers in their sealed chamber are paired with the 12" Scanspeak 30W/4558T00. This driver is classed as a Subwoofer by Scanspeak, yet some dealers list it as a Woofer. This is because it has a usable range up to 1000Hz, this is way beyond what most true sub drivers achieve, they tend to roll off at a much lower frequency. This is also one and a half octaves above my planed crossover frequency, which is pretty much ideal.
My Yamaha NS-1000M have an F3 of 53Hz in a 50L sealed box. The Scanspeak driver calculates (Qtc 0.707) with F3 of 38Hz in a similar sealed volume. If I keep the foot print dimensions the same, I'll be able to use the 300mm stands I made for the Yamaha's with the new speakers.