The way I see it there are 2 options to keep this plant growing, but both are going to involve cutting the top back. First, I need to point out one important fact that makes this possible: Banana plants are not trees. Trees are woody perennials. Bananas are herbaceous perennials, much like any perennial garden flowers you might have (hostas, daylilies, daffodils, etc). All the top growth can be replaced every year if it needs to. What appears to be the 'trunk' is just a series of overlapping leaf sheaths. If it's cut back within a few feet of the ground new leaves will grow out from the roots and grow right back.
So, you have two options: One is that you can cut it back to about two feet and tuck it in a cool corner until spring. It will produce new leaves when you put it out in warmer weather. Another option is to plant it outside. If you do this you'll want to watch for the first frost. When that happens the leaves will all die off. At that point, cut down the 'stem' within 2-3 feet of the ground and wrap it in burlap, bubble wrap or similar, then mulch heavily over the roots to protect them from the worst of the winter freezes. Mulched properly, the roots can safely tolerate air temperatures down to -10 degrees Fahrenheit. In zone 6, that pretty much doesn't happen. In spring, the plant will put out new leaves from the base. If you decide to plant it outside, site it somewhere with well drained soil and full sun.
