I've had an unshielded tower speaker directly alongside my equipment rack (including the 950) for years now - I don't believe that it would pose a problem to locate a sub next to the equipment rack.

Is the sub's driver actually firing toward the main speaker, or is it a downfiring sub? I'd be less worried about inducing vibrations in the main speaker than I would in restricting the sub if the speaker is too close and obstructing too much of the sub's driver.