The cable change for OSD makes me wonder if the old composite was a bit less well shielded, but that's just a guess.

Does the distortion happen with sources other than cable? There's a chance that you're simply noticing a calibration problem (similar to what we often see and adjust on computer monitors). The only way I could see any of your new gear producing a condition like that would be unshielded speakers interfering with the TV tube, and the Axiom center (only one close enough to do that) is shielded.