You're confusing materialism with substance realism. Not all substances are material. As I state in one of my excerpts, Aristotle himself admits an immaterial, immovable substance. Materialism is opposed to idealism. Modified realism, including but not limited to traditional substance realism, is opposed to radical relativity.
Modified realism is on a deeper level than materialism versus idealism.
Modified realists can even offer merely pragmatic reasons for what they take to be real. In fact, they don't have to offer any reasons at all. Modified realism is not defined in terms of the reasons one gives. It's defined as a very general type of view one may or may not hold, for any reason or for no reason. This sort of specifics would not make any difference to my basic views.