First of all, our own M3Tis sound better to my ear.
That would put you in agreement with those suggesting that the richer sound of other speakers is elevated bass. The difference between the M3 and the M22 is a broad 2-3db hump centered around 100Hz.
The difference between the M22 and M22+ sub is bass extension down to whatever the -3db point is. There is lots of bass between 40 and 60Hz in all music and even down into the 20s in some.
The first case, the M3 is an exageration of the bass in a certain range. The second case is the sub providing sound that the M22 cannot produce.
