Your stem seems much too short and high to me already. More back angle is better for your back because that substitutes flexion for compression in the spine. Just because you're touring is no reason to adopt an uncomfortable position. Cycling is very good back exercise. That said, you might need more specific exercises to create a stronger core. Consider buying a copy of Core Advantage.

This is what it's supposed to look like:
https://www.youtube.com/watch?v=z04uoO7U_SA
http://www.bikeforums.net/road-cycli...l#post12953035
http://www.bikeforums.net/long-dista...l#post12207030