I'm looking at changing the set-up about a bit if I do I would probably end up selling the KI as I would not have anywhere else to put it, probably try at work first, how much should I be asking for it?
Chances are £100 max - probably less. The 6000KI didn't get such a brilliant write-up in comparison to the others in the range and was probably around the time Marantz saw their crown for midrange gear start to slip. See what it's going for on Gumtree or Ebay to get an idea of where you should be aiming it at in the used market.