Hello, leenia.

According to my chart, your McSpadden dulcimer (DAA) should work with strings of .21 or .22 on the low D and 2 x .14 on the As - so that's only a potential thou difference on the low D. If you really want to double up the pitch on the first two strings, try 2 x .14.

The Cedar Creek (GDD) is only slightly shorter, just shy of 98% of the vibrating string length of the McSpadden (DAA). You don't say what gauge of strings are on it, but I can't see how even the thinnest strings will work at that high pitch. You describe the sound as twangy - surely it would be very tort indeed up there. If you want to tune it DAA, try a wound .20 on the bottom and 2 x plain .12 or .13 on the middle and top.

If you can't buy a set with those gauges, string websites sell loop strings singly. In my experience, it's worth experimenting, as even 1 thou can make a huge difference in playability if you're sensitive to string gauges for particular styles of playing.

On another note, I'm trying to understand how DAA on the dulcimer works. DAD gives you an open drone on the root and 5th when playing on the fretted top string, your most basic playing position. DAA, assuming A is your root, gives you an open drone on the 4th = D, which puzzles me. I expect, therefore, that your root is on the third fret of the top string (assuming a diatonic dulcimer), which gives you a run-up which could work nicely, but you already have that on the second string. I'd be intrigued to understand your playing technique.   

Hope this helps.