The fermenter would probably not be a problem, but you will have an issue when you go to secondary fermentation. There would be an awful lot of air space between the wine level and the bung/airloctk. I would try to get something smaller in place of your 6 gallon carboy. Maybe you could find a few 1 gallon jugs.
I believe it's ok to do primary ferment with a lot of head space, but after that it would be best to limit the space. Like getting some 1 gal. Jugs to secondary and finish up in.