Hi, I am quite sure something very similar can be done, but to come REALLY close to it by programming, very much try and error will be needed. The PC3 can build new samplesets out of existing material inside the ROM. something like this might be needed to get close to that chiffy sound. Since the D50 scales down just one short sample over rhe entire keyboard, a very typical effect happens, that sounds like that in lower notes. To get that, most likely it is necessary to build a new scale with just one sample.
You might get less close to that with mixing an analog brass (there is one in the PC3) and that chiffy sound in the set of GM-sounds. Might be a start. More editing needed.

You are right. The Standard GM Soundset has a Calliope/Chiffer sound, but the Forte does not contain a GM Soundset and it seems to me that there is also no ROM Sample which has this characteristic Flute Attack Sound that is needed in order to build a convincing Flutish Brass.

I don´t know exactly about the Forte. People tell it can reproduce (very much) the same like the PC3. Restrictions mostly with demanding setups as far as I remember. Since the synth-engine was told to be the same (?) it "should" have the same capabilities and also the same sample-set. Maybe the GM set is just not loaded, but could be loaded. You need a copy of the factory soundset of the PC3 and check for those sounds. The Forte can load single sounds out of a bunch, does it?
And again, at least the PC3 can take that sample of the chiffy sound, "rip" it apart and build a new multisound (a sample or more divided over the keyscale) out of it. It can even take just a part of it and edit it like a sampler would do with a freshly sampled signal. It´s one of the most astounding abilities by the way, and hardly used. No other rompler can do that as far as I know. The "Dreamer"-sound is done that way. It´s a new wave built out of an edited one in the ROM of the synth.
However, maybe the Forte is able to load such a sound, done on a PC3. I don´t know if the same work can be done inside a Forte. But the Chiffysample at least "should" be there. I don´t know I am no pruduct-specialist.

THX for your advice. I will give it try and post the result soon. In the meantime I found a chiffer/flute sample in the ROM
Still if somebody already got the job done I would be glad to let me know.

I will post the my attempt on the flutish brass as soon as it is possible. Right now the Forte only can save all user data at once. It is not possible to save a single patch to disk. I guess this will be possible when the sound tower sound editor will be available. Or have I overlooked something?

Sorry, dunno.