Hi tyros2009,
The software you are talking about is called "
Tyros3 VoiceEditor" (only available for Windows PC). This program is included on the data
CD that comes with the Tyros3. To my knowledge, the program is
not available as a download from Yamaha. But if necessary, I can upload the "Tyros3 VoiceEditor" for you. Then simply get in touch here again.

With this PC Voice Editor you do NOT create "
User Voices" (e.g. .vce), but so-called "
Custom Voices" (.uvn/.uvd).
User Voices are created directly on the T3 by storing modified Preset Voices in the VOICE SET. (Note that
User Voices can only be used in
keyboard parts, not in Styles or MIDI files.)
Custom Voices are created by importing
new samples (wave files) directly on the T3 and mapping them to the desired keys.
You can then "fine tune" these Custom Voices on the PC Voice Editor (e.g. with regard to envelopes and/or effects).
You can also use the PC Voice Editor to
create Custom Voices from Preset Voices (or the waveforms/samples of the Preset Voices). This is probably the function you mentioned, because here you can combine up to 8 so-called "Elements" (which can come from different Preset Voices). You can also create Custom Voices that combine
Preset and
new samples.
By the way,
Genos and
Tyros5 use the "Yamaha Expansion Manager" (YEM) to create Custom Voices. Here, too, you can combine Preset and new samples if required and use up to 8 "Elements" per Voice.
Unfortunately, with
PSR-S and
PSR-SX models, you CANNOT create Custom Voices (in YEM) that are completely or partially based on PRESET samples (but you can only use NEW samples here).
Best regards,
Chris