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The instrument known as Celesta... Although many call it a Celeste.

There are two Celesta sounds, not sure what "bill" you need these to fit.
If you have the S90 XS/S70 XS EDITOR, you can try tweaking them to make them fit the bill for your requirements. Otherwise... sorry, you don't find them appropriate for your needs.

If you need a real one, Yamaha makes them (custom builds them, wait time is 3-4 months)
🙂 I got to play one of these several NAMM shows ago, and they are quite unique (and expensive) instruments. (Curious what about the Celesta in the S90 XS misses the mark for your purpose?) If you are trying for a less pure Celesta sound you might substitute the Glockenspiel waveform or try mixing it in at an appropriate level _ but true Celesta have a surprisingly pure bell tone.

http://usa.yamaha.com/products/musical-instruments/keyboards/celesta/an_overview_of_yamaha_celestas/?mode=model

Thanks, I take your point that it's not a question of what the instrument is "called" since a celesta should be a correct name. Still 1) on other synths the sound I'm looking for in my mind's ear is "celeste" and more importantly 2) those two voices, which I do have, sound too fake or electronic to me to use in this case. The specific application is the song "Pity the Child" from the musical Chess, which opens this Friday. The opening sound is indeed supposed to sound something like a child's room as the character describes his angst which he attributes to his upbringing, and the two voices you mention didn't sound pure enough to me. So I tried E. Piano 1 but my conductor isn't happy with that one. Of course I could let him hear what you mention, or yes I could try to edit one of the two we're talking about it. Any thoughts? It was a surprise to me as the other legit piano & keys sounds in general are terrific.

The Celesta, to my ear, is extremely accurate (sounds very much like the $30,000 instrument I played), perhaps what you want is more of a Toy Piano tone, and not a Celesta at all. I made the suggestion of blending it with a Glockenspiel - which will definitely give a more Toy Piano tone. The nice thing about having a synthesizer is you can program it.

Place the two Voices together in a PERFORMANCE and use the PART Volumes to create the balance you require.

Thanks much - the music director and I will start by looking at the Celesta voice, maybe he'll like it better than my first impression, and we'll go from there with your ideas.

Perhaps if you raise the Resonance knob, up to +24, you might like the way that affects the Celeste sound in the GM bank. Another possible music-director-pleaser might be the Music Box Voice, two buttons to the right of the Celeste. That sounds very real to me too, depending on exactly what you are looking for.