Just in case, did you verify that the existing cable was in fact a pin to pin connection and not a transposed connection? Seen it before with some manufactures.
Apart from that I don’t have much; I’m surprised that it would not show a picture in some fashion.
I would second the check the original question cable comment...
Also, I stand by my original comment-at those frequency's cross-talk is going to be your biggest problem. Not just shielding the cable itself but shielding each line from the other lines.
Yeah, I walked the original cable with a multimeter... didn't SEEM to have any cross pins. Unless something connected to 2 pins, but I kind of doubt that.
I'm thinking maybe it's simply too long? Wonder if I should just cut it, resolder in the middle and see if it makes the situation better or not.
justchat: good point re: crosstalk, but I'm not sure how to avoid that - that will be the case for any ribbon cable, no? So maybe the cable choice is wrong from the start - but I'm not sure how to dodge that problem, since I _need_ a flat cable for this.