Buying better cables is always a good idea, even if they don't solve the immediate problem they will prevent other problems later on.
If new cables don't solve the hiss problem, try these things:
1- Make sure the phanton power switch is turned on when using the Apex mic, it needs 48V to work properly. You can turn it on or off for the dynamic mic since they just ignire phantom power.
2 - Are you using the same gain setting on your pre-amp for both microphones? You may have too much gain selected for the Apex mic, which will raise the noise floor and create hiss. Try lowering the gain and moving the sound source closer to the mic so you don't need so much gain.
3 - Move the mic pre-amp as far away from your computer as possible since it might be picking up noise from the CPU. You might try moving it around while connected to see if the hiss gets worse when it's close to you closer to your CPU.
That's all I can think of, hopefully someone else will chime in.