I disagree they have to be the same. If they play up high crossing near 300Hz then yes, they need to be the same, and in placed under the main speakers in stereo. But that's usually called a woofer, not subwoofer which is usually <80Hz. If you're just playing to 80hz or lower, they don't need to be the same. There isn't so much tonal information down there, mostly just fundamentals, which is why we can tolerate subwoofers with THD of 10% and it still sounds good. Try that with a tweeter where all the harmonics are that determine tone quality, and where 0.1% THD is intolerable.
Exspurts say that having subs of different designs and placed randomly around the room (electronically time delayed to match 1st arrival time of the main speakers) is the best way to minimize acoustic modes in the room.
IMO, the best subs for "high-end" music listening will have very large cone, large powerful motor, large sealed sturdy cabinet with lowish Qts like .57, very high power and high damping amplifier - and having many of them (to increase total cone area and minimize cone excursion and distortion at given volume level.) Bass is by far the most difficult and expensive register to execute well in a home stereo system, but it offers the most valuable opportunities for upgrades.