Thanks for the additional information. It provides some scope to what you have and what needs to improve. Your current system uses somewhere in the ballpark of 350-400W when loaded. At 400W, your Earthwatts PSU is ~80% efficient, so it's drawing 500W from the wall.
A quick look at new system power: CPU (77W), everything else but a graphics card (~50W). So, call it 130W.
GPU: The GTX 275 idles at 50W and uses 140-200W at load. A modern card with similar performance will idle at 10W and use 55W at load. You can't disable the graphics card. You can use the Virtu s/w that comes with most boards to utilize the iGP for non-gaming tasks. But, my guess is your DAW s/w will eventually use gpu acceleration...which puts you back onto the graphics card.
Lower TDP CPUs:
I'm also in the "don't bother" camp. A modern CPU quickly ramps up it's clock and core voltage to do a task and then ramps back down to idle. At idle and low load, you'd never notice the difference in power used between a regular and lowered TDP part. At high load, the regular part will finish the task quicker. Besides all that, 12W is spit in the wind when compared to total system power.
Looking at Passmark CPU Benchmark, the dual Xeon
is 4328. The low end i5-3330
($190) comes in at 5910. So even without hyperthreading, you should see a bump in performance. If you go up to the i5-3570
($215) it's 6998. Moving up to an i7-3770
($290) with hyperthreading the score goes up to 9451. So, figure out how much a bump in horsepower you want for what price.
Mobos: I like the Asus IVB mobos for their fan control. Just sort through the H77 boards and maybe the lower end Z77 boards to find the features and I/O you want and while you are there take a look at the reviews. They are a useful indicator of happiness as well as defective return levels.
RAM: Probably want to go with 2 sticks of RAM to make use of dual channel memory performance.
CPU cooler: I like the Thermalright TRUE Spirit 120M ($40) + a ~$10 better fan.