I've heard others complaining about poor TBS-6983 driver as well. Both windows and linux users. Not unusal for TBS to release problematic drivers. Bug reports all go to /dev/null.
There will likely eventually be an alternate driver created for this card. I think the guy who put out the open source TBS-6925 driver is saving up his paypal donations to buy a 6983. Until then you can try posting bugs on the TBS forum, but I wouldn't hold your breath.
CrazyCat has patched up the windows driver quite a bit already. Could watch his linux-tbs-drivers fork on bitbucket.