Here's a total different take on it. Not sure where you live, but if you live in the USA call Frank at Audioworks (203) 876-1133 get his best price on the Tyros 5. Once you're satisfied with his price, then sell the S950 and the Tyros 4. I have the feeling that you will come ahead with a bit of cash profit. I use Craigslist to sell my arrangers when I want to upgrade to a newer model and usually get a good price, but I will admit I'm about a 55 minute ride from Boston where there's a huge potential market to sell to. If you live in a small town away from a big city, you may not have as good luck selling on Craigslist. I like Craigslist because I meet the buyers in person accept cash only and in a public location. I sold my T4 in the lobby of the bank building I worked in. There was power to let the buyer test drive and plenty of people walking in and out to ensure both the buyer and myself were protected from being scammed/ripped off. I have also met buyers in Dunkin Donuts, Panera Bread, the parts department of a large Toyota dealership and Uncle Tony's Pizza ( not our Tony Mads).
Of course another approach sell the s950 then try the or maybe the Korg PA900. Although I'm enjoying my T5, it was the 76 keys that sold me on moving up from the T4, had it not been for 76 keys I would have tayed with the T4. Good luck you have a few options.