"Japan was ready to surrender before the atomic bombs" and "Japan surrendered because of the USSR's declaration of war, not the atomic bombs" are two completely different arguments.
To spell it out for you: Japan was ready to surrender before atomic bombs, but held back because the allies terms were unacceptable, and Japan were hoping to get better terms, using USSR to mediate them. Only when that hope was removed (by USSR declaring war on Japan) did Japan realise they had no other choice. And then they actually surrended.
"[Before the atomic bombs were dropped], the Imperial Japanese Armed forces were already signalling a willingness to end the war, with the one condition that the Japanese emperor ... would not be harmed."
I don't know why you're trying so hard to read things that are not there.
Japanese surrender was not prompted by bombings of 6th and 9th August -- they had endured already much worse bombings of their cities during that summer, and were not particularly scared of atomic weapons.
However, Japan was very scared of USSR, who up until then was neutral against them. All that changed rapidly and hugely, when USSR declared war on Japan, and attacked Manchuria on 12:01am 9/August.
Check the timelines -- the argument is solid and much more compelling than "Japan surrended because nuclear bombs".
https://foreignpolicy.com/2013/05/30/the-bomb-didnt-beat-jap...