"Keep in mind that the Soviets had been successfully battling the Japanese in China and Korea ever since Germany's surrender."

That's actually not true. The Soviets did not invade Manchuria and Korea until after the declaration of war on August 8, 1945.

"The surrender message itself by the Emperor was unheard of since the Emperor never spoke to his people. The Atomic bombs were what convinced him."

The evidence is actually contradictory on what convinced the Emperor. In his address to the Japanese people, he did mention the bombs, but in his address to the military, he mention the Soviet invasions and not the bombs. It's possible that the combination of both persuaded him. I don't think we'll ever really know for sure.