The details were in a memo from the president's Chief of Staff, detailing McArthur's accounts of five separate surrender offers. This article gives more details and a lot of sources:

http://www.ihr.org/jhr/v16/v16n3p-4_Weber.html

In an article that finally appeared August 19, 1945, on the front pages of the Chicago Tribune and the Washington Times-Herald, Trohan revealed that on January 20, 1945, two days prior to his departure for the Yalta meeting with Stalin and Churchill, President Roosevelt received a 40-page memorandum from General Douglas MacArthur outlining five separate surrender overtures from high-level Japanese officials. (The complete text of Trohan's article is in the Winter 1985-86 Journal, pp. 508-512.)

This memo showed that the Japanese were offering surrender terms virtually identical to the ones ultimately accepted by the Americans at the formal surrender ceremony on September 2 -- that is, complete surrender of everything but the person of the Emperor. Specifically, the terms of these peace overtures included:

- Complete surrender of all Japanese forces and arms, at home, on island possessions, and in occupied countries.

- Occupation of Japan and its possessions by Allied troops under American direction.

- Japanese relinquishment of all territory seized during the war, as well as Manchuria, Korea and Taiwan.

- Regulation of Japanese industry to halt production of any weapons and other tools of war.

- Release of all prisoners of war and internees.

- Surrender of designated war criminals.

Is this memorandum authentic? It was supposedly leaked to Trohan by Admiral William D. Leahy, presidential Chief of Staff. (See: M. Rothbard in A. Goddard, ed., Harry Elmer Barnes: Learned Crusader [1968], pp. 327f.) Historian Harry Elmer Barnes has related (in "Hiroshima: Assault on a Beaten Foe," National Review, May 10, 1958):

The authenticity of the Trohan article was never challenged by the White House or the State Department, and for very good reason. After General MacArthur returned from Korea in 1951, his neighbor in the Waldorf Towers, former President Herbert Hoover, took the Trohan article to General MacArthur and the latter confirmed its accuracy in every detail and without qualification.