@britesynth - 15k will not get you very far since a mobo and cpu will already set you back about 9k. That leaves you very little for other peripherals unless you are going to re-use some peripherals like drive/s, burners, and the case. It's often recommended to use at least 500w PSUs with the newer boards even though they are energy efficient; most audio computer have at least 2 hard disks and burners as well as lots of ram and an efficient fan system, so the PSU wattage is justified.
@Peter North - it depends on your mixer configuration. Some 24 channel mixers come in 4-buss or 8-buss configurations which can help you with your soundcard choice, e.g., pair a 4-buss mixer with a 4-input soundcard. I still maintain that if you can afford an interface with at least 8 inputs, the better - you never know when the additional inputs will come in handy. There are loads of firewire interfaces out there from Presonus, Focusrite... even A.R.T. has the Tubefire which pairs 8 of it's TubeMP preamps with a firewire interface. Even Phonic has a firewire mixer similar to Alesis. For the record, we have used an Alesis FW Multimix8 with no problems other than 8 channels is too limiting for our needs - ask xjepoyx for our experience with the Multimix.