Apologies to Norah Jones, I needed more bass!

@billpete  - In this particular case I tried to balance sensitivity and power.  With dual woofers in parallel I get 90 dB sensitivity (for 2 watts), and a maximum output around 110 dB/1m with a little wattage left over. 

@erik_squires So, to do that, you need an active crossover? 

@billpete - Not sure what part you are referring to, but if  you ask, did I use an active crossover to triamp?  Kind of. :)  I actually use Hypex 2 and 3 way plate amplifiers which have built in DSP capabilities which includes filtering.  Specifically the FA123 and FA253.  

It does help that because I use no passive crossover I don’t have the usual power losses associated with them, either directly through resistor padding or indirectly through the losses of the frequency shaping filters. 

@billpete  - It may help you to see the wiring.  Take a look on my blog, the second picture shows how the amp is mounted on the back of the woofer section and how it connects to the mid and treble on the bookshelves. 

This saves me a great deal of device and wiring complexity.  I have 1 wire from the HT processor to the back of the plate amp, then short speaker cables to the top section.  This is a lot simpler than a "discrete" setup using a stereo crossover, plus 3 stereo amplifiers.  Talk about messy wiring! 

@billpete - Going back to your comments about power, using active crossovers changes the power to voltage relationship.  Power is proportional to the square of the voltage, so a single amp that has to do midrange and treble and bass must be rated much larger than it would if it did them separately.  

In other words, if I attempted to do this with a single mono amplifier it would have to be rated at well over 1,200 watts, much more than if we add the 3 amplifier sections together to 600W.  At my listening levels and music and movie tastes this is all serious overkill.  I doubt I hit 20W.