Comparing the two both in a 3.8 cu. ft box 20x30x14 tuned to around 40-44 hz. Tone is very close to being the same. What stands out on the 2-pi is the silky treble and maybe a little more Fat on the low end. Not much if any volume difference.
On the 3-Pi's more true to life mid range. This is at a normal volume range around 1 watt average. When the power goes up the 3-pi's impact or dynamics start to prevail above 10 watts or more. OK I prefer to build both of them. They are both High Fidelity.