Build a shuttle box (Score 1)

Sounds like you want and maybe need a turn key solution that is cheap. But as they say, Fast, Cheap, Reliable... Buffalo LinkStation Quad could be an appealing solution. It gives you Time Machine for your macs, but is probably a dog with datasets larger than 1GB. At a 1GB file size, smallnetbuilder.com shows write speeds to be 11.4MB/sec. If and when you do ultimately decide that soho solutions can't give you the speed you need, be sure to load the pc with as much RAM as it can take. Ample RAM to cache the file system can either maintain or reap huge throughput gains.