Engineer In The House?

Big favor to ask: Would somebody with an electrical-engineering background take a look at Colby's design for an active-mixer circuit at http://www.nirvis.com/mixers.htm. A couple of questions: 1. If I want to build this for five inputs instead of three, what component values should I change? 2. Will 15 vDC from an unregulated power brick do the trick for this circuit, or should I use a regulated power supply instead? If the latter, know any good sources for pre-fab power modules to incorporate into do-it-yourself projects like this? I've tried Radio Shack and they're a lost cause.