When evaluating a 5.1 audio amplifier, you must prioritize Total Harmonic Distortion (THD), which should ideally be less than 0.1% to ensure high-fidelity sound. The Signal-to-Noise Ratio (SNR) should be above 90dB for clear audio output. Additionally, verify the RMS (Root Mean Square) power per channel rather than peak power to understand the true continuous output capability. For modern integration, ensure the unit supports HDMI 2.1 (4K/120Hz or 8K/60Hz pass-through) and decoding for formats like Dolby Digital, DTS-HD Master Audio, or Dolby Atmos if backward compatibility is required.