Rick, it has been noted in this forum quite a couple of times, that DNS-323 actually IS pretty slow. Under perfect conditions (e.g. copying of one large file) you can get around 15MByte/s, that's it. Under normal conditions I would expect no more than 10MByte/s.
Now your actual problem comes from MacOS's Finder and (I guess) especially from Spotlight, both of them scanning all the files in a directory more or less completely. Now devide your 500GByte by 10MByte/s....
I'd suggest first of all to stop Spotlight from indexing the NAS shares and furthermore (if possible) stop Finder from scanning all the files, creating individual thumbnails and so on. If you list the directory contents of the shares on the command line you won't see any delay here, I guess.
As for the "unsupported drives" these could only be an issue if they have 4k-sectors. In that case you find loads of information in the pinned thread on top.
And to be honest, it is really no surprise an external HD connected by FireWire beeing significantly faster than a network storage, is it?
Just my 2p,
grixx