I can help you on this Mel, it's simple.
I have a Rio 300 with said background and had the same concerns until the EX1200 turned up.
The loop at the top of the inlet and outlet pipes (it's actually not a loop but a right angled bend) is just long enough to be able to fit in the two holes at the back of the tank and hang over the 3D background.
I have the inlet pipe on one end of the tank (concealed within the Juwel internal filter column, which I kept in for added filtration). It would be even easier if you didn't have the filter column there but works fine either way.
I then have the outflow pipe at the other end of the tank, the spraybar is attached to the glass at the side of the tank firing a good old current the whole length of the tank (you can of course reduce this if need be). The suckers have quite long extensions allowing just enough for the spraybar to reach the side of the tank.
The spraybar length is adjustable as well. I think it comes in three bits - angled bit to attach to outflow pipe, middle and ednd with the stopper. I just took out the middle bit and it fits just fine.
I had exactly the same concerns as you but it fits fine. The backflap of the Juwel multilux light occasionally sits up literally a millimetre or two if it gets propped on the inlet and outlet pipes at the back but no big deal and if you just apply a little pressure to the top of the pipes you can get the flap flush.