We report a cw optical parametric oscillator (OPO) in a novel architecture comprising two nonlinear crystals in a single cavity, providing two independently tunable pairs of signal and idler wavelengths. Based on a singly resonant oscillator design, the device permits access to arbitrary signal and idler wavelength combinations within the parametric gain bandwidth and reflectivity of the OPO cavity mirrors. Using two identical $30\mathrm{mm}$ long MgO:sPPLT crystals in a compact four-mirror ring resonator pumped at $532\mathrm{nm}$ , we generate two pairs of signal and idler wavelengths with arbitrary tuning across $850–1430\mathrm{nm}$ , and demonstrate a frequency separation in the resonant signal waves down to $0.55\mathrm{THz}$ . Moreover, near wavelength-matched condition, coherent energy coupling between the resonant signal waves, results in reduced operation threshold and increased output power. A total output power $>2.8\mathrm{W}$ with peak-to-peak power stability of 16% over $2\mathrm{h}$ is obtained.