I'm a newbie to the field and would appreciate the advice.
My 5.1 speakers: Infinity Beta 50 - front, C360 - center, ES250 - Surround
left and right, SW-12 - sub.
I wonder if I have to upgrade the receiver Onkyo TX-SR501 to get most of
them? My room is 11'x11' with open left and right walls.

I would suggest a Denon AVR-3805 or 2805. I have a crappy sony
strede695 that I caught for cheap off of ebay. I am glad I didn't pay
allot for it because SOny is basically underpowered and overrated. But
the Denon has the best sound and features compared to the Onkyo. The
2805 is a little cheaper and may be right for you.