need or not need 6.5 fret
Instruments- discuss specific features, luthiers, instrument problems & questions
As mentioned above, you don't "need" a 6+ fret. It may be handy, but you don't NEED it, and some of the best players ever do not use it. NO traditional tuning requires a 6+ fret (1-3-5 or other modern tunings may, but I don't know them well enough to say so). The dulcimer, without any additional frets, works just fine as long as you are willing to accept it for what it is, and not try to make a guitar out of it.
If you are buying older instruments by "name" builders, you are probably best off not adding a 6+ fret (or doing any other tweaking of the fretboard, as doing so can seriously affect the resale value of the instrument, no matter who installs the fret. If you have a Warren May instrument that does not have a 6+ fret and you just can't do without one, even having Warren install the fret will affect the resale value if someone is looking for "style X" and finds it but with a 6+ fret that should not be there... If you want a Warren May with a 6+ fret, buy one of his newer ones with that fret, don't mess with an older one.
You asked "How hard is it to find another note, like middle 9 in place of the 6.5 when playing in DAA? Where else would I find the note to replace the 6.5 in other tunings?" That is your challenge, should you choose to accept it, Grasshopper.
updated by @ken-hulme: 01/03/16 10:59:22AM