Regarding eyewitness accounts of Omdurman: dozens of published and unpublished accounts of the Battle of Omdurman are listed in my British Military Operations in Egypt and the Sudan: A Selected Bibliography (Lanham, Md.: Scarecrow Press, 2008), ISBN-13: 978-0810859548. I would provide more details, but my books are in my household goods, currently being shipped on a slow-moving banana boat across the Pacific to Seoul, South Korea, where I am now.
You may also be interested in my piece "Death in the Desert: Peake's Artillery at Omdurman, 1898," Soldiers of the Queen 139 (December 2009) -- and this includes encouragement for all VWF members to join the Victorian Military Society and receive -- and consider contributing articles and book reviews to -- the outstanding quarterly issues of Soldiers of the Queen.
Happy New Year!