A pair of REL subs will provide the upgrade sound that you are hoping to achieve.
Depending on the nature and and musical venue you prefer to listen to, I would not think it would be necessary to go beyond the "T9/x" sub. A pair should yield improvements to you overall system that other brands can only aspire to. Of
course REL has several other sub lines that have won virtually every audio award the industry has to offer. If you have the funds, you might explore that course.
I can assure you that a pair of "T9/x subs will rock your world, and at the same time, provide the finesse that classical and jazz music require.
AXPERT