Sorry for the big bump but...
Have you looked into the thread about overriding EDID information?
http://www.widescreengamingforum.com/forum/viewtopic.php?f=64&t=17635
also recommend doing a google search on modifying EDID as it appears that somehow the incorrect information is being passed by the adaptor or there's just some corruption of the EDID information in general as resolutions that should have no problem being displayed aren't working right?
This looks like the most promising solution for me but that link is dead (something to do with the forums newer SEO URIs?). Does anyone have a working link? Searching for EDID masks gives almost no relevant hits on Google. :(
Thanks for any help, been at this 2 days straight now!