An updated version of the XP-ALL build document is now available here;
http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=48463&g2_GALLERYSID=26da524b522cb1f3b2e1f96b873230ae (http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=48463&g2_GALLERYSID=26da524b522cb1f3b2e1f96b873230ae)
It now includes a new section on the XP-ALL+ mod (single 27C1001 EPROM), regaining the loss of stereo sound in XP-100 mode, and a correction to the output volume mod (regarding pot type, and grounding point).
As always, any questions, problems, document bug reports, etc, address them to the XP-ALL build troubleshooting thread.