difference between 8ohms and 4ohms and voltage con

voltage makes no difference. The 8 vs 4 ohms is a reference to your speaker's impedance. You can tell by looking at your speaker's impedance spec. Typically they're rated at 8 ohms, often 4, and it's not uncommon for them to be rated 6 or some other value. Keep in mind this is a minimal rating and the true impedance varies with frequency.

In any event, it's not something you need to worry about.

I understand that 8 or 4 ohms will make no difference but it may for the converter and then ultimately for the amp. A 550W converter can handle 160Wpc not 320Wpc. If the converter cannot handle it, it will fry the amp. Anyway, I will check my speakers to see. Thank you.

You need to look at the voltage data on the rear of the amp or manual & see what the maximum wattage consumption/draw is.
Should say something like 120V, 60HZ, 950 watts. The 950 is max draw in my example.