Media share from USB only?

[cpt_paranoia]

Yes.
Disable the media server (Settings/Media/Media Streaming/Off).
Mount the USB drive, and locate the share created for it.
Enable media serving for the USB share (Shares/[share]/Media Serving/On)
Disable media serving on all other shares.
Enable the media server (Settings/Media/Media Streaming/On).

More detailed information on optimising the Twonky DLNA media server can be found here:

'[FAQ] Twonky DLNA Media Server Setup & Use

Some Frequently Asked Questions Regarding Twonky, And Some Answers The MyCloud includes a Twonky DLNA Media Server. Sadly it doesn’t seem very well integrated into the MyCloud, and the two fight for supremacy. I’ve spent a long time trying to understand how it works, and reading the forum, I see many other people also have trouble with it. So I thought that, rather than trying to answer these questions individually, I’d try to write an FAQ covering the things I’ve found, and the problems I or …