I think you have to decide between two competing forces: one the one hand, publishing a DRM-free ebook makes it easy for people to obtain it which hopefully diminishes copying. Ease of use and ease of purchase drive sales. On the other hand, if copies are made and you do not follow up with takedown notices, you will see a bigger amount of unlicensed copying. Going with a bigger vendor reduces this significantly, but that's what you pay the hefty fees for. If you're selling a $200 textbook, you probably need protection. if you're selling a less than $5 ebook, you probably should just self-publish and admit that some people will copy it. Middle ground is to get the book on the apple store, on kindle store etc.
Yes, I suppose you are right, it is a difficult balance, as once you put the work out there, it is too late to take it back.
It is a permanent choice. Your words had the ring of sensible, so I will think on it and see how things progress.
K
P.S. Thanks for the input and the time to help.