I've been priviledged to actually meet with Jack Bybee, developer of the famous Bybee Quantum Purifiers (http//www.bybeeinside.com). Jack has some thoughts on power supply issues that are technically sound. You should email him and seek his opinion(s) on power supplies. I haven't had a chance to talk with him about PC-based music servers, but I'm sure his depth of knowledge and wisdom would be very helpful.
I can tell you that you should really get a good PC power supply that is both efficent and quiet first. http://www.silentpcreview.com recommends the Nexus PC PSUs for their stable power delivery under load and silent performance. You can find some great deals on the Nexus PSUs, hard drive noise reducing cases, fans and heat sinks through http://www.siliconacoustics.com/. Only after you upgrade your PC PSU should you start looking into a power conditioner and UPS unit.