Watch the Drop 3 Voicings: online guitar lesson by Brad Carlton from Guitar Lab: The Golden Arp
The drop 3 voicing of the Add 9 chord in 3rd inversion is probably not one you'll use much, but it warrants some examination. It is derived from the 2nd inversion close voicing of the Add 9 chord and two layouts are produced. The form involving strings 1, 2, 3 and 5 is a bit impractical, but the other form has a great sound to it. Be cautious about potential intonation issues and watch the lower registers as it could become muddy. Remember that in the keys of A or D, the open E (6th) and A (5th) strings could be used as the 4th voice (5) of these forms.