Krasnaya,
I'm afraid that some of your beliefs as to the japanese being willing to surrender if the Emperor was guaranteed to remain, is quite incorrect. There's a good piece in many U.S. newspapers editorial page today that shines new light on that issue from declassified (since 1995) intercepted messages the Japanese diplomats sent to each other in July, 1945. There's something like 1 million messages the "Magic" system intercepted, and they DO mention that the diplomats DID know we had already offered the retention of the Emperor, and they still ruled out unconditional surrender, but opted to wait for a better deal. They figured that once we invaded and suffered immense casualties, that the american public would pressure the government to make a quick deal to end the war before Japan was conquered. Truman and the Joint Chiefs had thought we'd face only 3 Japanese Army divisions and, at the most, 2,000 aircraft. We then learned that the Japanese had moved 10 divisions to the area and that the country still had approx. 10,000 aircraft at its disposal. The U.S. Navy, faced with those new figures began arguing against an invasion, and instead was pushing for a blockade and aerial bombardment.
I'm sure, faced with this new intelligence, as well as a rift among the Joint Chiefs, we can more easily see why Truman made the decision to go ahead with the A-bombs, since we never really got the story behind his decision.
Much of the info in today's article was also verified today by my father-in-law, who had survived (barely) Iwo Jima and was training for the coming invasion with his fellow Marines. He knew then about the Navy's reservations and their pending coming out against the invasion.