how can I programm 16 voice or just more than 4 voice in performance mode??

By definition, (means: this is how it is) a “Voice” is single playable sound. As many as four Voices can be combined by placing one in each of the four Parts of a “Performance”. A Performance is defined as four Parts mapped across the Keyboard in Layer fashion, and/or Split, or a combination of Split/Layer. A Performance Part, since all four can be triggered together, can be played directly or assigned to respond to one of four available Arpeggiators.

A “Mixing” (found in Song and Pattern modes) can contain as many as sixteen Voices by placing one in each of the sixteen Parts of this program. There are 64 Mixing setups in Song Mode and another 64 in Pattern Mode. Unlike Voice and Performance modes, each Part of a MIXING can be set to any MIDI Channel, 1-16. In Voice and Performance Mode only one MIDI Channel is used.

If you want to play all 16 MIXING Parts at the same time (?) you can place them all on the same MIDI Channel.
Song Mixing and Pattern Mixing Programs can be named, stored and recalled when desired (whether or not you use the Sequencer). In these modes you transmit from the Keyboard via a Track of the Sequencer... the Midi Channel of that Track determines what gets sent to the Tone Generator.

In the [SONG] > [MIXING] > press [EDIT] > press the Track button [1]-[16] to view the Part parameters.
Press [F1] VOICE > press [SF2] MODE > here you can the Receive Channel of the Part.
Repeat for each Part by moving to that Part.

If you were to set six Parts to RcvCh =1, then when Select Track 1, you would be playing all Parts set to Receive data via Track 1.
By default Track transmits on Ch1, Track 2 on Ch2, Track 3 on Ch3 and so on, This is also programmable