Here i'll list some useful links to useful information over internet related to audio design.

LM317/337 regulator performance tweaks/analysis:
http://www.tnt-audio.com/clinica/regulators2_impedance1_e.html
http://www.tnt-audio.com/clinica/regulators_noise1_e.html

Active filter design:
http://www.linkwitzlab.com/filters.htm