Noise from the tank will definitely be an issue. I used to have an fx5 running in my bedroom on a 125, and that thing was annoying. I had to start running a hepa air filter to use the white noise to drown it out (the fan noise of the air filter was constant, the filter noise was a much more annoying slight grinding). filtration, water noise, etc. on a 240 will be even worse.
Currently I have a sunsun 404b (525gph) filter near the foot of my bed and it's pretty quiet- I would recommend this over an fx6 if noise is a concern. They are also cheap and work well, and they have a built-in UV light. I would recommend you run 2 of them on a 240- which would still be cheaper than one fx6!