I had a an SB 1000 - not bad for $600
I replaced it with a Dynaudio 18s - $1800. This is a non-ported design with dual opposed 9in drivers. The improvement was dramatic. The tonal definition of different types of bass instrument is much clearer.
The dual drivers mean that zero vibration is transmitted to the floor on which it is placed - all the sound all comes through the air - transparent and uncolored.