I doubt it was something wrong with the cable if as you say, you've tried different ones.
The easiest way to see if it is a phasing issue is simply just to have a listen.
When you sit down in front of a well set up sound system, you should be at the corner of a triangle with the speakers at the other corners, each one being exactly the same distance from you, and both pointing towards you. Then you should hear a 'stereo image' which involves sounds appearing to come from in-between the two speakers. Play music on whatever DVD player you use (in speaker 2 mode, NOT anything else!), and then on the BeoSound and compare the sound produced by both. If the sound from the CD player sounds 'vague' and you can't seem to point at where the actual sounds are coming from in between the two speakers, while the DVD player seems to position things perfectly in between the speakers, then there is a phasing issue.
However, if both sound very similar in terms of where sounds are positioned between the two speakers, then the issue is not phasing, but more likely to do with the way the surround sound processor is working (or not quite working!) in the TV.