Ian-
When you hang the Europas (which to my knowledge would be a first!) there are two important considerations beyond safety and the method of hanging:
How to tilt them to aim the time-coherent axis down into your workspace.
The length of the hanging pendulum.
For the first- consider a metal shop bends and drills a piece of 3/16" cold-rolled steel flat stock at least 2" wide into a flattened "U" shape, so that it either comes around the sides of the speakers from the wall and bolts into the marble (we can advise on the size of bolts, etc), or comes down over the top of the speaker from the ceiling to touch each cabinet side. This "U" bracket would need to be mounted to at least one wall stud or ceiling rafter with two 1/4" lag bolts. Secure the speaker with steel cabling from the hardware store, of course.
For the second- if the pendulum length is longer than 12 inches, then the resonant frequency will be so low that the speaker may move with the music- specifically at a 1Hz or so resonant frequency. This tone is not in the music directly, but is there by the way of difference tones- like the beat frequency that emerges while tuning two guitar strings.
Consider the swing arms designed to hold flat-screen computer monitors- they would allow you to swing the speakers out from the wall, and then tilt them down and toe them in. When you are done, push the Europas back up and in. I believe Parts Express and MCM Electronics has some of those available, and I have a master catalog here somewhere from the leading mfg if that helps. There are many styles and weight capacities.
Once you decide, consult with me directly on the size of the bolts/screws into the Europas. Because the cast marble can be unforgiving, specific screws must be used, and their pilot holes into the marble must be the correct size.
Best regards,
Roy Johnson
President/Product Designer
Green Mountain Audio