Subwoofer for Phillips MFB541 Active speakers

Greetings, l have just purchased a pair of Phillips MFB 541 Active speakers and am quite impressed with the sound quality (especially given the low price paid). lm interested in attaching a subwoofer to the speakers but really have no idea if and how this can/could be done. An comments and advice would be greatly appreciated.
Provide a link to the speakers and list your system components and you'll likely get some assistance.