SMPS for stereo audio amplifier
Overall it seems OK.  The 500kHz switching frequency should help with noise, although you can always add a second inductor/capacitor stage for further filtering.  As long as you don't end up with broadband hash in the output due to noise in the regulator, and as long as it doesn't oscillate, I suspect you'll be fine.

Layout will be critical.  You really need to think like an electron to keep the supply stable and to keep it from radiating.