It is not the size of the driver on the SVS. They all sound similar regardless of driver size. We can speculate as to why that is - whether SVS has chosen to do this or they simply don't know better. They definitely are not musical. Fundamentally, they lack articulation. The sealed Axioms do not. You'd have to be deaf to not hear this difference.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated