This theoretical paper explores how researching the identities of musician-teachers can be differently conceptualised through a critical posthuman lens. Wider calls to action demand an expanded professionalism of musician-teachers, but when such recommendations are combined with fixed notions of identity as self-contained and producible, they risk becoming essentialistic and exclusionary. Foregrounding the intricacies and tensions in locating the teacher subject therefore posits a need for theories of complexity and becoming. Barad's agential realism provides an onto-epistemological shift, such that the musician-teacher is not separable from the world, but intra-actively comes into being through a relational ontology, exposing identity as a mechanism of capture through series of agential cuts. These material-discursive entanglements and performativity of the dichotomous musician-teacher role are then discussed. By thinking difference differently and addressing relations of power, these have ethical implications for research and what comes to matter, drawing on non-representationalism and signalling post-qualitative methodologies. This philosophical framing does not serve to reduce complexity, to figure out what works, but rather stays with the trouble -- the messiness -- by arguing for future empirical work that is inclusionary in the widest sense and grounded in the embodied, affective experiences of musician-teachers themselves.