What’s the difference between the front and rear panel headphone outputs

Symphony Desktop's headphone outputs employ a zero-ohm driver design that ensures the best performance with any headphone available today, regardless of the headphone’s impedance. To best match the sensitivity of various headphones, Symphony Desktop offers two headphone outputs with different power capabilities:

• Connect higher impedance headphones (30 ohms and above) to the front panel headphone output. This output can drive virtually any pair of headphones.
• Connect lower impedance headphones to the rear panel headphone output to ensure the lowest noise and best power handling.