Super-Poussin (the ReadyNAS add-on expert who contributes to the ReadyNAS forum) has very kindly built a Twonky 5.1.3 add-on for the ReadyNAS Duo and NV+. The add-on comes with the standard Twonky trees and now has the defaults (contentbase and contentdir in the twonkymedia-server-default.ini file) preset to better suit the ReadyNAS.
I've written a long post on the Linn forum to help folks decide whether to use this version or not. There are links to the ReadyNAS forum page (to download the add-on) and also links to my custom trees. My post also gives instructions on how to install the add-on and tips on optimizing it (the RPC call to mask the local loop-back address suits all versions of Twonky 5 and has also been proven to work on other products like the Thecus 5200 pro; post here) .
Note that the add-on comes as standard (i.e. as Twonky intended it to be) and will thus be suitable for Xbox/PS3 users etc. If that's you, stick with the standard Super-Poussin supplied add-on and don't use my custom trees as they'll possibly cause problems.
See here for the long (and very tedious) post