not knocking FF's speaker systems, but this is me and I'd try the -cheap- route first for more bass. MCMelectronics.com 8" 10" 12" (whatever fits) treated paper cone cloth surround woofers are good for 93-97db SPL from the 1st watt of audio power (depending on size-diameter).. VERY efficient and replacing just the woofer, is cheapest quickest and easiest. about 2x louder bass than a typical woofer that'll give 88-90db from the same 1st watt. cheepo backbox speakers are usually pretty well mated to the machines amp section, might be just fine left in place.

you'd get more from a powered sub of course, if you dont mind using another electric outlet for something on the floor to sweep or vacuum around with wires hanging down from your machine to feed it.. depends on how much bass you feel the need for I guess, lol.

the inexpensive MCM woofer can add more bass pretty painlessly:
their 8", http://www.mcmelectronics.com/product/55-2950 (94db?!)
their 10", http://www.mcmelectronics.com/product/55-2951 (95db?!)

their 4-ohm versions perform about the same if the original woofer is 4-ohm, you can, same price.
best bang for the buck that I've seen yet, after LOTS+LOTS of looking. inexpensive but real nice.