Cureent state-of-the art for DAW desktops... how quiet?

If as close as zero noise as possible is important to you, I know that Studio Cat will build systems with fanless power supplies and fanless CPUs.

http://www.studiocat.com/index_files/Page423.htm

Whether you really need it that quiet only you really know.

I built my own DAW and the only thing I can hear from about 3 feet away (if I struggle) is a very slight amount of PS fan noise. Any farther than 3 feet and I can't hear a thing. I don't know what the actual noise floor is but it's low enough to not bother with measuring the noise floor or spending another penny to try to reduce it even further. I haven't heard a hard drive make any mechanical noise in years. My daughter's laptop makes more noise than my DAW. And that punk rock band playing in the other room - well forget it

btw - a mic will pick up fan noise easily. But a little noise gate or exander usually takes care of that. I have these Oktava MK12 mics which are very unforgiving of fan noise. In fact, if there is even the slightest amount of breeze from the fan (I'm talking about a regular room fan), the mic will pick it up and make it sound like a low rumble. Those Oktavas don't want anything to do with breezes. I wouldn't even think of using one outside without a wind screen or pop filter. I gave up worrying about room noises a long time ago. Except in very rare circumstances nothing ruins a mix.

You can always go liquid-cooled, which can be virtually silent. But they are a real pain, and I wouldn't recommend that route unless you really need total silence.

Fortunately, most fan noise is high-frequency and therefore easily absorbed. Enclosing the computer in a solidly-constructed (screws and glue) box made of 3/4" plywood lined with 1 or 2 inches of 703 will probably make it as quiet as you need. Just be sure to have adequate ventilation so the computer doesn't overheat. Air intake and exhaust vents should be wide, include at least one 90-degree bend, and also be lined with acoustical dampening material. An iso box like this can be constructed for about $40, which sure beats buying a new computer just because it has quieter fans.