12 Hz!! I believe you have a beautiful piece of kit! Man, I want to be rich...
Well, as I said, you can buy Sennheiser HD600 headphones (or even the new HD650s)
and a good headphone amp, all for the same price as a pair of B&W603s. So you don't have to be rich - you just to have to care more about being able to hear 12Hz than you care about being able to hear 44Hz through speakers.
You'd have serious problems finding stereo speakers that can go down to 12Hz. There are very few which even go as low as 20. (B&W's £11,000 Nautilus 800 hits -6dB at 25Hz). There are plenty of subwoofers that can't usefully go that low. This forum used to be madly in love with the Velodyne HGS-18. It is/was one hell of a subwoofer, and many people felt it was good value at a bit over £2000, but even that's only officially rated down to 14Hz. If you want to spend £15000 on a Velodyne 1812, that'll take you down to 7Hz, but not many people have that kind of money.
Come to think of it, if you've got £35,000 to spend on a pair of the original B&W Nautilus speakers (not forgetting that you will need no less than eight top-notch monobloc power amplifiers to drive them, which will cost several thousand pounds each) that will get you down to about 10Hz.
The best recording I have ever come across for headphone listening is this one: (
click here). It is actually designed to be listened to on headphones, and the soundstaging is a bit odd on speakers. But any good-quality recording of the same pieces made using a good organ (the sort of thing you'd find in a cathedral or a really big concert hall rather than your local church) should similarly be thrashing the 16-31Hz range.