So... I set about undertaking some exhaustive digging last night for a suitably sized and reasonable quality replacement for the original HK speakers, and after plenty of frustrating dead ends, I came across what with any luck should be able to be fitted as a direct replacement into the HK enclosures (which are an important factor in getting so much sound out of so small a driver) with minimal modification if ive done my math right... and best of all, when fitted they would visually be indistinguishable from the stock speaker, as they have a metallic parabolic cone like the HK's. I tracked down a relatively local supplier so I intend to order one to experiment with and see how I go... will keep y'all posted.