Disable thumbnail generation in finder
I don't know if this will work in your particular case, but you might as well try it.
Open the Samba share and press Command+J, then uncheck "Show icon preview" and click on "Use as defaults". This way the Finder won't try to extract info from the file to generate a thumbnail, no matter if it is an image, or a mp3, or a movie. However this would be valid only for the root directory you just changed the settings to, so the local hard drive stuff should be ok.