Hi and a welcome to our little engineering world. 
Let's see what I can come up with.
6th Army was strictly a Pacific-based unit! I am printing this here for the benefit of all readers. Here's a FEW links regarding:
This is a nine-page PDF file - ARMY ENGINEERS IN POST-WAR RECONSTRUCTION: THE PHILIPPINES, JAPAN, AND GERMANY, 1945-1947
by Dr. William C. Baldwin - Office of History - Headquarters, U.S. Army Corps of Engineers
This document discusses among other things, how in the fall of 1944 MacArthur redeemed his well known pledge to return to the Philippines when he landed on Leyte and that on Jan 9, '45 the American Sixth Army landed in northern Luzon and moved south toward the Philippine capital, Manila.
http://www.hq.usace.army.mil/history/Philippines%203.pdf
Amphibian Engineers - A site dedicated to the soldiers of the six Army Engineer Special Brigades.
http://ebsr.net/ESBhistory.htm
Sixty years ago, on March 11, 1945, General Douglas MacArthur landed on Corregidor after forces from General Walter Krueger's 6th Army had liberated it...
http://www.americanthinker.com/2005/03/nor...to_victory.html
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The Sixth United States Army was a field army of the United States Army. It was activated in January 1943, commanded by Lieutenant General Walter Krueger. Under the code name Alamo Force, it assumed control of the majority of US Army units involved in Operation Cartwheel, the campaign to isolate the neutralise the Japanese base at Rabaul in New Britain. Following the completion of Cartwheel, Sixth Army joined Australian Army and other US forces on the north coast of New Guinea. Similar in conception to the island hopping operations of the central Pacific, the object of the attacks was to land, establish a garrison and airfield which could support the next strike, and then move on. In September 1944, Sixth Army was released from operations in New Guinea by the US Eighth Army. On 20 October 1944, X Corps and XXIV Corps, under Sixth Army, invaded Leyte in the Philippines. By December, Leyte was almost secure, and Sixth Army was relieved again by Eighth Army to prepare for the invasion of Luzon. As a prelude to that invasion, the island of Mindoro was invaded by the Western Visayan Task Force comprising the 19th and 503rd Regimental Combat Teams. Luzon itself was invaded on 9 January 1945 by I and XIV Corps. Sixth Army units fought south until they met up those of Eighth Army advancing from around Manila. Sixth Army then continued to clear the north of Luzon until the end of the war. Sixth Army was to have provided the ground forces for the first phase of the invasion of Japan, but the surrender changed that. Occupation duty then followed for a short while until Sixth Army returned to the United States. Sixth Army then took responsibility for training of Army forces from part of the continental United States until it was inactivated as part of force reductions.
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United States Army in World War II
The War in the Pacific
Triumph in the Philippines
by Robert Ross Smith
http://ibiblio.org/hyperwar/USA/USA-P-Triumph/index.html
I would contact the Army Corps of Engineers Office of History for more information on the 6th Army Order of Battle, etc. Please see my Research section for phone numbers, etc.
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15th Corps WWII
http://en.wikipedia.org/wiki/XV_Corps_(United_States)
XV Corps breakdown
http://www.history.army.mil/reference/ireland/niob.htm
