I've noticed that a few people have looked into some more 'offroad' capable tyres for the DD in the past with mixed results. I was up for a new set of hoops recently and found a pair of Dunlop D616's for a great price so thought I would give them a go. They are very different tyres with a super aggressive chunky treat pattern. Wet grip is amazing (compared to the stock Pirelli Diablo 3's), but turn in is noticeably slower. They are very stable in the turns however and still sporty enough to cope with decent lean angles. I haven't tested them out on any gravel yet but by the looks of them they will be at least *better* than normal road tyres if their wet grip is anything to go by.
I reckon they look pretty cool too.