I traded my 6600 for a 7700. Then I traded my 7700 for the 8900. But all my machines were well-used. I'm not going to be much help on exactly how much money you should get for your 6600. To me it is a matter of how much am I willing to pay for the upgrade and the new features. I sew almost every day and the features on the 8900 have been well worth every penny I paid. My dealer tends to throw "extras" into the deal, rather than come down on the price. Last year at the Des Moines Expo Janome was offering to throw in a 3160 with the purchace of an 8900. Good Luck on the trade.