Hi goldorak,
You are right, there are some amps and receivers that allow you (by a small rear switch) to change the voltage from 120 to 220 volts, from the voltage selector. Some even have another special switch that permits you to change the 60hz running rate to 50hz. But usually, just changing the voltage, automatically adjust the running rate (Hz).
I've seen some Yamaha model receivers like that in the past, cannot remember the exact model # though.
Also, some brand of receivers allow you to change their voltage and running frequency rate, by removing their top cover, and then switch to the appropriate voltage by an internal slider or switch.
* Table of general power supply:
1. U.S.A. & Canada: AC 120V/60 Hz
2. Singapore: AC 230V/50 Hz
3. Australia: AC 240V/50 Hz
4. General: AC 110/120/220/240V 60/50 Hz
Yours applies to #4 (General: 220V/50 Hz).
* Some multi-voltage models (Pioneer receivers included), are provided with these switches. But U.S., Canadian, European, U.K., and Australian models are not generally provided with these switches.
And the ones that do provided them (two) are the type that have a slider switch, with one side at 110V,120V-127V, and the other side of the slider at 220V,240V. Then you have another switch, where you need to use a screwdriver, and turn it to the same position as the slider switch, which is 220V-110V-120V~127V-240V.
** I know that I do have some components at home with these type of switches, but I just cannot remember which ones.
>>> Now, you finally ask me about the Onkyo TX-SR876 (which I own),
vs. the Pioneer Elite SC-05.

Well, goldorak, if you've been reading some of my previous posts from other threads, you already know my answer. I did mentioned it several times, actually make this, multiple times, in various threads.
Briefly, the 876 is a true power house, with all the features that your heart can wish for.
The SC-05 is a very nice looking receiver, also an excellent value for it's heavily discounted price. But ultimatly it simply does not reach the same goals than what the TX-SR876 was built for.
My best regards to you & say Hi to your family & friends in Lebanon from me,
Bob