OK, the speaker arrived, there are a few differences between the standard Superb speaker and the one from the L&K model. The cone is slightly different in appearance, the roll suspension on the L&K is both larger and more rubbery and the magnet is around 25 mm larger in dia, otherwise is the same. Fitted it the same way as the old was, with pop rivets and the difference in the quality between having a woofer and not, in a single door is staggering. I don't think the bass is quite as deep with the standard speaker, but I'll gladly make do with it as L&K model cars are extremely rare indeed on the road, out of 301 registered in 2013, 274 of those are still on the road. The 27 not on the road may just be stored in garages somewhere, not written off, but if I can get a proper replacement at a sensible price, I'll take it, so if anyone comes across one, I'd be grateful if they could let me know.
The saving grace with bass is that it is not as directional as mid-range to high frequencies are, hence why some sound and cinema systems only have 1 subwoofer between 5 sound channels.