It's nowhere near sounding like an original grand and I see a lot of room for improvement which is why I call it a work in progress. Still, I'm really satisfied with it.
Ok, I worked on it some more. Added a couple more operators. Tried to add some flavor to it. Here's an update: http://soundcloud.com/lainalain/grand-synth-piano-update
Some suggestions to make it somewhat more realistic, if that's what you're after:
On a real instrument, the amplitude envelope varies with pitch, becoming faster with higher pitches - in the case of a piano, the envelope gets roughly 50% shorter for every octave up you go.
The lower-end notes are all single-stringed, but the mid-range are double-stringed and the high end are triple-stringed, and for multi-stringed keys, the strings are slightly out of tune with each other - and the more strings a key has, the lower the sustain level is. The bass strings are also wire-wound, which greatly strengthens the higher partials.
Finally, the overtones of struck and plucked strings are not perfectly harmonic, so it may help to slightly detune the modulator or carrier.
