Talking about PSR-S970 Vs PSR-S975 (Voices)
While viewing the specification chart
In S970
989 Panel Voices, 41 Drum/SFX Kits
Featured Voices:
131 S.Art!, 30 Mega Voices, 31 Sweet! Voices, 74 Cool! Voices, 89 Live! Voices, 30 Organ Flutes!
In S975
1090 Panel Voices, 55 Drum/SFX Kits
Featured Voices:
140 S.Art!, 30 Mega Voices, 32 Sweet! Voices, 74 Cool! Voices, 99 Live! Voices, 30 Organ Flutes!
So in S975 there are 101 additional panel voices, 14 additional Drum/SFX Kits.
In featured voices 9 additional S.Art! Voices, 1 additional Sweet! Voice, and 10 additional Live! Voices. But the Mega! Voice and Cool! Voice are same as S970.
So there won't be any new Mega Guitars, Mega Brasses and Mega Choirs given in TYROS5.