meistah

i posted about this on another forum, but didnt get much help..however i have more ideas about it now... i got a set of computer speakers (edifier s5.1) i find the speakers themselves to be more than adequate, and the sub is very musical, however the subwoofer is very lacking in volume and spl, and i believe due to its tuning sounds horrible on certain notes, so i want to improve on it in the most inexpensive way i can... i was thinking i could build a sub in a box with a plate amp, and hook it right up to the sub input on the sound card, then just have the edifiers go to the rest of the inputs..which i know is very ghetto but i think it would do what i want it to do... my other thought was to just get rid of the edifier system and go with the sub/plate amp and new speakers...i have 2 focal ca130 coaxial speakers which are awesome, but im not sure what id do for power/control of them...i dont really need surround sound so ultimately 2 speakers and a bigass sub are just fine for me.. any way i cut it im going to want a new sub and amp...as i really like mach5s stuff i was thinking of going with one of their subs and the 300w plate amp on their site...thought it would be really awesome to do an 18" with that amp...but im worried that while it will be powerful, it wont be tight and musical enough, as ive never heard an 18" sub before...i know their 12 would be fine in a sealed box, so i might go with one of those...im very open to suggestions