FIXED!!! - for me at least..
So I have found a solution that works in my situation.
The problem was NOT with the NAS but with my Verizon FIOS router. (Needless to say, tech support of Verizon could not come up with anything more creative than "change the wi-fi channel" to help me and then tried to sell me a premium tech support service.)
So I came to think that for some reason the Verizon Fios router was blocking DLNA on the wireless side (it would work on devices wired via ethernet.). That made me wonder if there was a way I could access the dirve wirelessly but bypass the Verizon router.
So I dug out an old Linkysys wireless router I had lying around and followed these instructions on how to use a router as a Wireless Access Point (WAP):
http://www.smallnetbuilder.com/wireless/wireless-basics/30338-how-to-convert-a-wireless-router-into-an-access-point
I now have the NAS plugged via ethernet into the Linksys. Any device that uses DLNA connects to my network via that router. And everything is working like a charm.
I know everyone has different setups, but hopefully this may be useful to others having DLNA issues.
Good luck
Ian