I have a Dune BD Prime 3.0. i have full 35-40gb mkv files, which have a dd5.1 640kbps track AND lossless FLAC (i use xbmc on another machine) with the english .sup (subtitles) all straight from the blurays and the dune works perfectly on them, both over SAMBA (windows shares) and NFS (which i no longer use, because samba is fast enough.
i even have a test file which peaks at 68 (or 78, i forget)MBitspersecond and that plays fine too.
If i was buying again, I'd go for the Dune Smart, because it takes up less space, but otherwise, i think it's great.
EDIT: if you're player is realtek based, get Hanewin NFS server, and set that up and you'll get 50Mbps files working fine, but the test file above (higher bitrate than Bluray goes still stuttered).
Also, if you have FLAC tracks, the realtek seems to work harder and is happier with dd/dts/aac5.1 soundtracks.