well... I haven't looked for a Theramin among the Integra sounds. It could further approach it to the original. But there is a genuine female opera voice in the original. This voice sample is far from perfect, originally it is from a Roland expansion of the mid 1990s. But I don't know any other instrument that would have a female solo voice sample like that at all. The versatility of the Integra is impressive.
BTW, the chords are damn complex, I played them by ear, but there's still one chord I haven't completely figured out.