MASSIVE X requires an AVX compatible CPU. AVX, or 'Advanced Vector Extensions' are extensions to the X86 instruction set architecture for microprocessors from Intel and AMD. AVX compatible processors were introduced in 2011 by Intel and AMD.
MASSIVE X requires an AVX compatible processor to provide increased performance. Its audio engine provides advanced wavetable oscillators, unison voicing, a flexible audio router, and other features which make the use of AVX necessary.
The installation of MASSIVE X will be blocked on non-AVX-compatible systems.
Here you can find a list of compatible CPUs with AVX.