Just found the speaker part numbers for HK audio. Quite a pricey doo as you could imagine- but may be worth getting one rear mid-range to test if it actually works before getting any more of it.
I think i'd probably upgrade the front mids and add the tweeters..
Tweeters: £97.68 inc VAT
Window sills for tweeters: £49.20 inc VAT
Mid-Ranges: £128.36 inc VAT
Total: £275.24 inc VAT
The next step will be to buy the blaupunkt P&P amplifier