Speech-generating devices (SGDs) provide users with text-to-speech (TTS) voices that shape identity and self-expression. Current TTS voices enable self-expression but often lack customizable features for authentic voice embodiment, particularly for nonbinary SGD users seeking gender affirmation as existing TTS voices largely reproduce binary, cisgender speech patterns. This study examines how nonbinary SGD users embody, or disembody, synthetic voices and the factors influencing voice affirmation. Through a survey, we analyze experiences of nonbinary SGD users and their impressions of generated speech samples, investigating the role of technological possibilities in gender affirmation and voice embodiment. Findings inform the creation of more user-centered TTS technologies, and challenge dominant paradigms in speech technology, gesturing toward a posthumanist rethinking of voice as co-constructed between human and machine.