the way they get so much wattage is they use a switching supply (dc-dc converter) with the required output voltages. for instance, for a 200W (into 4 ohms) amp, the converter takes 12V DC, chops it at 50khz or so, and runs the high frequency square wave through a transformer which steps it up, and then through a rectifier and filter, and you get +/-65V out of the rectifier. this becomes the power supply for the power amp. additional secondary windings and rectifiers provide the +/-12V or +/-15V for the preamp and bass filters. be aware that although only about 7.25A is provided to the speaker (at 200W), the input current to the switching supply is over 16A. it's actually a bit higher because the power supply's efficiency is usually 85-90%. such a switching supply is not something for beginners, and will not work well with the amp you already have. you would be better off replacing the subwoofer with one that has a higher sensitivity than the one you currently have. i'm guessing that a Bose sub probably is rated about 80 to 85db@1W@1 meter. if you replace the sub with one that has a sensitivity of 90 to 95db@1W@1 meter, you have just increased the amount of acoustic power by a factor of 10, so if your amp is a 10W amp, it would be equivalent to replacing a 10W amp with a 100W amp.