Great book list! Must check them out soon.
Great book list! Must read them soon.
The context is informal, like a comment in a blog post. Is there any difference in the meaning of these two expressions?
No, these phrases do not mean the same thing.
In this context, "check them out" means "look at, and consider either downloading, borrowing, purchasing, and/or reading".
If the context involved a library, "check them out" might mean "borrow from the library".