can I use a subwoofer?

Asus p8z77-lx/Bheringer Ms20's active monitor speakers.I'm using the kit mentioned,just through the on board sound of the mobo,and upto date Realtek drivers and and overall happy with the sound,but for some ov my taste in music requires more bass,and was wondering could I add a sub?From what Iv'e read it is yes,if it is also active and just connect it to the pc/speakers as you would a conventional set ov pc speakers,with the only real requirement being active crossovers on the sub would help.The other way would be to pass them through a receiver.I would prefer not to go down the reciever route,if can be helped as that was the idea of the Bheringers.Please feel free to correct me if I'm wrong as like I said after wading through www land that seemed the most plausable answer from many,and am checking here.Ps the Bheringers rock..

how much money do you want to spend?
for under $100 you can buy a 'cheap' powered sub

Insignia™ - Rocketboost 6-1/2" 70W Wired/Wireless-Ready Subwoofer - NS-RSW211
then connect it to one of your mobo output jacks and connect the Bheringer's to L/R output jacks and use the Realtek control panel to set what jack does what--or--for several hundred dollars you could buy a 'better' powered sub with it's own L/R connections and low pass filter
Energy - 10" 400-Watt Powered Subwoofer - ESW-C10

and connect the Bheringer's to it

Ive got about £100 ish as far as connecting goes I take it I go about it as if they were regular pc speakers pc>sub>monitors?Ive got my eye on this http://www.google.co.uk/imgres?hl=en...&tx=118&ty=108.

should work--just remember to power on speakers after starting computer and power off speakers before shutting down as the resulting 'thump' can potentially damage your speakers

if im connecting the speakers to the sub I wont have to touch the sound manager cos there will only tbe one output coming from the mobo?did the Yamaha show up it shouyld be the Cambridge audio.Google Image Result for http://www.cambridgeaudio.com/assets/documents/SiroccoSubRear.jpg speaker will be on there own part ov the extension with there own on/off switch.

sorry--Yamaha sub showed when I clicked the link--then the Cambridge