Yep, I get what you're saying. It is possible for the CD changer to be connected and show the correct display on the HU without actually pushing out any sound.
That's why I recommended that you check your cables. I had previously used a hack posted on the forum where I could bypass my CD changer and DIY an aux input. The CD changer would still swap discs etc and the display would show the disc info.... the sound would come from my MP3 player. So, check your cables and ensure that everything is connected and matches up.
Fitting a Blitzsafe without further diagnosis will not fix your problem.
I can help with
* Reading Codes / Coding your car
* R&R FCAs, Tie Rods, Sway links....
Need an RTAB tool? Or clutch fan and water pump tools? PM me.