Sounds like you've already killed them to me. 6" plants won't go dormant, they don't have enough reserve in the roots. Especially tissue cultures 6" tall. If the seller told you to do them this way, then you got some bad info.
At 6" you need to keep them growing, or at least stalled where they are and still green. Keep them warm and in a bright area, allow soil to dry out between waterings.

You might have killed them as sandy suggested, but they may also be reacting to a drier climate in your house. I would also do as sandy is suggesting by keeping them warm and in a bright area, watering when the soil dries out. I've had a couple small bananas seem to die, but after a couple weeks, they came back and are now healthy and living outside here in Michigan.

The advise to overwinter them inside was good advise, if you want them to stay outside, wait until late spring to plant them outside.

jetlag98, your particular bananas need to be watered, given the conditions you describe on overwinterizing them. They are too small to be winterized in the no water-no light fashion. When kept in pots, water them only when the top inch and a half of soil has dried. This will prevent rot. Get GOOD draining soil as well. Bananas do not like to sit in wet soil when they are not actively growing in the winter. I would skip the trouble of a grow light. The sunniest window in house will do. They will more than make up for the growing in the summer. Also, when bananas get big enough, esp the ones that have been planted in the ground over the summer, they can be stored with no water and no light in a cool (not freezing) dark place. HOWEVER, in my experience with Basjoos, these particular kind of bananas are not BEST suited for inside storage during the winter. They are meant to be left in the ground assuming they are big enough and not 6 inches tall. If you wish to leave a larger sized basjoo in the ground during winter and don't want to loose any stalk height, I suggest that you read my (4th) post in this thread as this has worked for me:

Banana flower zone 6.

With Basjoos I do only one of 2 things for overwinterizing them. Too small, leave in window in pot and water very lightly. Too large for pot, click on link above and go from there.