The sides of the tv will be slightly over the edges of the cabinet perhaps but it won't matter it will make the display look even bigger i suppose as long as you don't mind the over the edge look. The tv in the image is probably 42"or 46". It looks like it's (the cabinet) is built like a tank by the looks of it... "Looks" being the word though, as it's a beautiful looking bench btw.
This is my older 50" plasma which is sold now, but my new one same size, will be sitting on this same glass stand and it's fine.
One thing I regret is hanging my TV a bit too high am wishing it was a bit lower in all honesty. Will make a point of measuring its mid screen height and let you know, but it does seem a little too high to me.
I've got mine on an Ikea cabinet that looks less substantial than that unit. The easiest way to test it is to simply stand on the unit and see if there's any creaking or give. If it can support your weight comfortably, it'll definitely support the D6900.
Compared to my previous 28-inch Sony Wega which weighed 55kg, the Samsung is positively lightweight - I think it's something like 30kg without stand, 35kg with stand.