Marantz 2270 + B&W DM2000: What subwoofer?

Hello all,

Long time reader, first time poster!

In the past year I've bought a Marantz 2270 receiver, and had it restored to new. I've had the extreme luck to be given a pair of B&W DM2000 (the ones with the pentagonal shape) by someone who just wanted to get rid of them.

The current set-up sounds good as it is, but I can tell something is missing. When I listen to other setups that tend to run for $1k+, I'm usually blown away by the clarity and definition of the sound that I hear. Maybe I am biased against my own gear (the grass is always greener on the other side), but I feel like there's something I could do to make this sound better.

Would I benefit from purchasing a subwoofer? I've done some research and come to the conclusion that I need an active sub, as I do not want to buy another amplifier just to be able to run it. If so, which active sub would pair well with the Marantz amp and the B&W speakers? I am open minded to suggestions, and if something interesting came up with a passive subwoofer, I would not turn it down.

Info:
- My budget for a sub is approximately $500. Willing to go a little bit higher if it's worth it.
- Currently residing in France.
- Would rather have the sub be vintage, so as to follow the rest of my gear.
- I listen to absolutely everything, from Metallica to Eminem, from Michael Jackson to Daft Punk, from Creedence Clearwater Revival to Queen. If possible, I'd like a sub that has flexibility.

I know those are a lot of restrictions, so please feel free to work around them. Thanks a lot!

~a grateful reader