This sounds like a file format issue or hardware issue.
Since the streaming works from the macbook we can elimite the PS3. the macbook and the wireless network.
What file formats are your videos stored in? If the file formats are not supported by the PS3 - like mkv/vob - they will need to be transcoded by the media server before being sent to the ps3. In your case the macbook is good enough spec to handle the transcoding, the processor in the lacie drive is not.
I stream to xbox/smartTV using serviio installed on my desktop. The desktop will convert xvid/mkv/vob files on the fly before sending them to the TV. This works because the dekstop has Core2Duo overclocked @3.4ghz with 4gb ram. Tried using an old P4 3Ghz with 1gb ram and winXP and it struggled with the larger, high quality video files.