A little googling on your part might have led you to the iOS app I found by googling a couple of years ago for the same objective as you have, and I found and use the perfect app to do what you want to do. In fact, right now I am using the app for listening to some new CDs I digitized tonight and put on my WDTV Live Plus drive less than an hour ago.
Have I piqued your interest? The program is FileBrowser from www.stratospherix.com/ , and no, it is not free, but if you can afford an iPhone and iPads, you can afford it for the few $$ it cost. So go to the site, check it out, and then buy it and install it so you can be using it.
FileBrowser is more than a music listening program, it’s like using Windows Explorer or Mac Finder, and you can play music, videos, photos, read docs, yada, yada. It finds EVERY drive on my network; even drives on my Pogoplug. It can be configured to use away from home via the Internet, but since I have a Pogoplug w/drives, and a drive attached to my router that acts like a cloud and an app for the router that is like having a remote NAS for my whole network, and other ways to get at my media at home and away from home, I have not set this up. I probably should, because FB is that good of a program, and I ought to use more of its capabilities.
And, then there is the free app, Twonky Beam. Since you are familiar with Twonky, you may have this app. If not, then get it. I listen to music with it when the PC on or off, and it allows me to play my playlist created with iTunes. Verrry nice app, but it cannot access shared drives like those on WDTV units; only those on servers such as Win7 PCs and such. It is installed on our iPhones, iPads and Kindles for streaming/playing music, videos and photos; plus wait, “there’s more”. Go discover it all.