We study a generic two-state model for an assembly of molecular motors which is described by means of a pair of integro-partial differential equations and leads to oscillatory motion in the presence of an elastic coupling to its environment. We discuss a reduction of the system to a minimal set of three ordinary differential equations that successfully capture the complex nonlinear dynamics of the full system. In the limit of high mobility and large elastic modulus, we report on the emergence of subharmonics in the power spectrum of the oscillations. This provides a rationale for the unexplained observation of secondary peaks in a minimal actomyosin system in vitro (Plaçais P.-Y. et al., Phys. Rev. Lett. 103, (2009) 158102), showing that the phenomenon is robust and genuine.