Take a look at the non-powered New Original Subwoofer by VMPS. It was designed to mate with the Quad ESL, and actually could be used as a stand for that speaker. Last I checked, VMPS subs could be purchased either pre-assembled or as a kit.
How low in frequency do your Maggies go? If you need the subwoofer to go any higher than 80 Hz, you will probably get better results with two subwoofers, one underneath each Maggie. This is especially important if you are you using your system for music rather than HT. You might be able to buy two VMPS subs for not much above $800 if you don't mind buying used.
If you want a true DIY subwoofer, i.e. you buy the raw driver(s) and design and build the cabinet yourself, you can chat with other such eccentrics (including myself) at www.diyaudio.com.
The large majority of subwoofers on the market are active (internally powered). I prefer passive (non-powered) subs. The internal amps included in active subs are generally of inferior quality compared to stand-alone amps. Also, the interior of a hot, vibrating subwoofer cabinet seems like the worst possible place to put an amplifier. My pre-pro does the crossover job, so I don't need a separate component for that. If you do need a separate crossover unit, they are available at reasonable cost from VMPS and many other sources -- or build your own, with a little help from other DIY'ers.
How low in frequency do your Maggies go? If you need the subwoofer to go any higher than 80 Hz, you will probably get better results with two subwoofers, one underneath each Maggie. This is especially important if you are you using your system for music rather than HT. You might be able to buy two VMPS subs for not much above $800 if you don't mind buying used.
If you want a true DIY subwoofer, i.e. you buy the raw driver(s) and design and build the cabinet yourself, you can chat with other such eccentrics (including myself) at www.diyaudio.com.
The large majority of subwoofers on the market are active (internally powered). I prefer passive (non-powered) subs. The internal amps included in active subs are generally of inferior quality compared to stand-alone amps. Also, the interior of a hot, vibrating subwoofer cabinet seems like the worst possible place to put an amplifier. My pre-pro does the crossover job, so I don't need a separate component for that. If you do need a separate crossover unit, they are available at reasonable cost from VMPS and many other sources -- or build your own, with a little help from other DIY'ers.