Brian,
DKVBrowser's handshake with the piano goes something like this (from memory):
a) Find the piano on the network (this uses a combination of a saved IP from the last time it worked, in combination with network plug and play [the piano announces itself periodically], and, if all else fails, DKVBrowser allows you to type in a hostname/IPAddress. You are clearly getting through this step.
b) Logon to the piano. This is an encrypted step where the client says it wants to log in, the piano offers up a challenge, and the client must respond with a key to unlock the door. Once that happens, you are mostly there, and DKVBrowser should mostly appear to be done with connecting. (I think you are stuck here).
c) Only after b is successful does the piano allow connection to the internal database. At this point, DKVBrowser can start populating the screen with albums/songs. I've seen cases where DKVBrowser gets through a & b, but appears "empty", indicating things failed here at "c". (I don't think you are making it this far.)
The fact that the app on your phone is failing as well gives me plenty of confidence to say that there's nothing wrong with DKVBrowser here. My first suggestion, if you haven't already tried it, is a hard power down of the piano. I've learned that all sorts of gremlins creep into this old software if it is left running for too long. If that doesn't work, I could work with you offline to see *precisely* which step isn't working, but even with that information, it isn't clear what the next step would be since Yamaha support remains mostly clueless at this level.
-Kevin