Originally Posted by
nomadmax
Change the stem for one with greater angle. A +17 might be a good start. Use this site to see how the higher stem angle will effect reach.
Stem Comparison Tool | yojimg.net
All that said, most of the time when people complain about low back pain it's because their low back is weak. Start with a stem and some back exercises before you go hunting unicorns. One last thought, I wouldn't do anything to extend the current steerer tube. IMO, that is just begging for trouble.
nomadmax,
Thanks a lot for your response. For instance, if I change the fork and install one with a longer steerer tube, will the drop from saddle to handlebar be less painful?
Additionally, the top tube size is 56cm and the current stem lenght is 9cm which is short for me. I would like to replace it with a 11cm deda newton stem.
My previous road bike was Merida Scultura (56cm) compact geometry, with a slight larger head tube (17cm). It was perfect for me.