Its NOT a fatal clash but the functionality of the 2 plugins is not compatible
admin-management-xtended allows you to quick edit author in the posts or pages list with co-authors-plus the ability is gone in quick-edit and one has to edit the post itself rather than the quick edit operations on the meta data
well that explains a lot – I had not dug into the source of either plugin
shame, because its often more convenient to edit the author etc. as metadata as a quick edit than dig into and edit the post/page especially when there are multiple posts to update.