Basically all line level audio cables are of coaxial construction, 75 ohms or not. There is no way to tell by just looking at a cable what it's characteristic impedance is unless it is clearly marked on the jacket as a 75 ohm type (such as RG59). Don't assume that just because a cable is "coaxial", that it has a particular impedance. RG-174 for instance is coaxial, but it is 50 ohms.