I haven't had much success on finding the difference between these amps. Are the Ti's just newer versions? If they are improved versions, how are they improved? Would I be better off using Ti's? I currently own a ZX 450, a ZX 500, and a ZX 600Ti. I was wondering if it would be worth getting a ZX 500...

The ZX450 sounds like a problem with a control pot. On those amps the crossover control will often cause the problem you are talking about. You can try turning it several times fully in either direction, then back to where you want it to see if the problem improves. You could do the same with the g...

I have 2 amps in need of repair.
A ZX 450 that I've owned since '98 that has channels cutting out.
A ZX 600Ti that I bought used 9 years ago that now pops when turned on, and fires my sub out of sync with music.

My priority is to get the 450 fixed 1st.