OK, got my model up (not for sale or viewing, just my own testing at this stage). I exported as X3D, zipped the files, uploaded, got errors back about size, figured out the hardwired defaults in the programs, needed to output from 3D-Coat with a scale of 0.0254 to OBJ, and then everything works scale-wise. Colors look good on the screen (of course, real test is printed...).
Price is high! $ 122.45 colored sandstone. I wish 3D printing were not so much. But it's a fully functional double flute in the key of high C (octave above middle C), now with decorations! Well, it was functional as a prototype printed on a non-color 3D printer of Zcorp, but it should be the same on the color one from Shapeways.
I will test some other flutes and costs and so forth - I have a lot of designs!
Now I also need to figure out the finishing and "food" safety (placing flute in mouth to play).
I wonder if Shapeways could offer polU or shellac or somekind of food safe finish....