If your goal to simply bolster your current presentation adding another -6dB Sub-Bass speaker should provide a noticeable difference.
REL, "subwoofers (I still like our original term Sub Bass System for its more complete description of what we do)"...
If you're interested in increasing the detail of the presentation as well as the addition of the delicate extra low fundamental frequencies found on many of todays modern recordings there are a number of economical -3dB subwoofer/s available. Positioning within your rooms standing wave bass mode/s, would be required for their optimum performance.
Actual subwoofers are adjusted, not matched, to integrate with any speaker choice.