I'm glad you figured out what works for you!

Helen has a great point - string gauge makes a huge difference when you tune an instrument down. Many dulcimer strings are quite light, and more suitable for higher tunings. If you tune them down, they'll be too slack and will often sound off pitch because they're sliding around so much. I've had pretty good luck with D'Addarios, but if you're keeping it low you may want to make up a custom set that's even a bit heavier. For that matter, a heavier gauge string may help the high notes sound better too - you just have to experiment to find the right gauge for you.

There's another issue on some dulcimers, though, which is intonation. Not a huge deal if you're playing very traditional style with the bass as a drone, but if you're chording it can be frustrating, and notes that seem to be in tune when played openly can sound flat up the frets. Depending on your instrument, there may be ways to compensate if this is an issue for you. Fro example, Warren May's dulcimers have a floating saddle which can be adjusted for proper intonation. Keith Young's had a fine tuning system.

Dan