Just a thought.....but what kind of chair do you use? For a friend of mine, it was her chair that was causing back pain. Look at how high you sit, what support your back has, and how close to the machine can you get? An adjustable height, rolling office type chair is what I prefer and I can adjust the height to which machine I am working with.
I have a Cloud cabinet for my Janome 15000 and when the machine is flush with the top of cabinet, the needle area is a bit far from me and I have to reach a bit farther to work. Kinda throws my posture out of position so I just get up more frequently to take the strain off my back.
Hope you find a set up that works for you.