The grills on M70s do come off -- the post and hole arrangement is really tight though, and you need to be careful because the particle board is made to be bent slightly so that there is a groove cut in it half way down and its all too easy to break the board when levering it off. You can pull the upper section out a quarter of an inch or so and then work down on one side then the other, progressively. The pair I picked up needed some tightening of screws, and the foam gasket on the back had decomposed, so that it no longer functioned as a sealed box. So I replaced the foam and while I was in, I noticed that the crossover had come loose on one side, so I hot melt glued it down. I had other problems -- one loose magnet on the phase coupler and both woofer terminals had decomposed, so there was a fair amount of work to get them up and running.
The M 70 is a 4 way, essentially a 3 way with a 'phase coupler'. The drivers are mostly or all seas and they are pretty nice speakers, if a little bland. You need DIN plugs to hook it up, though you could bypass them for banana sockets or some such.
