I do a fair bit of voice editing on
Ty2 although I've kept away from layering identical voices because "you can get undesirable phasing effects"- LOL!
The nearest I get is have say 2 trumpets panned hard to R & L (ie. not identical) but that gives a normal sounding trumpet.

For muted trumpet/trombone I normally use the DSP Talking Mod which does a much more convincing job than the default muted trumpet. Try it with the SA TrumpetFall.

Also use of filter can give a wider range of effects. Put Brightness at -51 & Harmo. at 44 on the above and you get a very soft muted trombone sound goo d for romantic ballads.

If the S900 defaults are set like Ty2 you'll get best effects by also pepping up the strength and touch response of individual voices using the onboard editor.

John