Atomic sized two-level systems (TLSs) in dielectrics are known as a major source of loss in superconducting devices, particularly due to frequency noise. However, the induced frequencyshifts on the devices, even by far off-resonance TLSs, is often suppressed by symmetry when standard single-tone spectroscopy is used. We introduce a two-tone spectroscopy on the normal modes of a pair of coupled superconducting coplanar waveguide resonators to uncover this effect by asymmetric saturation. Together with an appropriate generalized saturation model this enables us to extract the average single-photon Rabi frequency of dominant TLSs to be Ω0/2π≈79 kHz. At high photon numbers we observe an enhanced sensitivity to nonlinear kinetic inductance when using the two-tone method and estimate the value of the Kerr coefficient as K/2π≈−1×10−4 Hz/photon. Furthermore, the life-time of each resonance can be controlled (increased) by pumping of the other mode as demonstrated both experimentally and theoretically.