I already gave some reasons. The Panentheist god is not the highest conceivable being and not a maximally great being (not the Yahweh of Scripture). Panentheism teaches that the universe is inside God, and consequently evil and the devil are in God, which is impossible for the highest conceivable being of classical theism. Also, it would mean that God cannot think faster than the speed of light since the universe is inside him. There are several problems with Panentheism, and I can recommend numerous books refuting it. Some schools of Wicca, Buddhism and Hinduism believe in Panentheism. In the case of Wicca, the universe is inside the goddess. That Wiccan's believe in Panetheism, see Hawkins, "Witchcraft: Exploring the World of Wicca," pp. 34, 35.
Excuse me, but how can the Orthodox be closer to Wicca than Thomas Aquinas and the Christian Bible? Admittedly, Wiccan's accept the goddess, but nevertheless, the parallel is creepy, even though the Orthodox put their own twist on Panentheism. I'm assuming that the philosophical arguments against Panentheism would also apply to the Orthodox version, but this is what I am trying to find out.
The Panentheist god is the god of pagan Greek philosophers, not biblical theists. Here is more information against Panentheism.
Matt Slick on Panentheismhttps://carm.org/panentheism
Dr. William Lane Craig on Panentheismhttp://www.reasonablefaith.org/panentheism
A more detailed refutation of Panentheism by Dr. Norman Geislerhttps://www.jashow.org/articles/uncategorized/panentheism-part-1/
Geisler has a whole section on Panentheism in his "Encyclopedia of Christian Apologetics," page 576. You might also see chapter 12 of his book, "Christian Apologetics." (second edition), and the following:
Geisler, The Battle for God: Responding to the Challenge of Neotheism;
Gruenler, "The Inexahustable God: Biblical Faith and the Challenge of Process Theology":
Own, "Concepts of Deity"
Brown, "Process Theology and Christian Thought."