Hello! after listening music through full range headphones and realizing how I miss the low freqs in my otherwise great sounding stereo, I am thinking about completing it with a subwoofer. Now, I got a couple of Castle Richmond 3i and the Azur 640 cd-p and amp. What should I be looking at? I would love to own the Classic sub from Castle, but it is out of question... in the following year at least. Too much for my pocket! So the questions are: 1. How much should I spend to get a decent, musical subwoofer matching the quality of my present gear? 2. Is a passive subwoofer an alternative? It would be cheaper, and I have been told it is better when all the membranes are driven by the same amplification. Answers are welcome. Thanks!