Does the middle way apply to objects as well as the skandhas?
The middle way -- between annihilationism and eternalism -- does apply to objects. Objects are neither existent nor not existent. They are interpretative imputations made on the basis of multiple causes and conditions temporarily coming together in their non-stop motion, transformation, and interaction.

Objects we have consciousness of are not "made of" substance, according to Mahayana Buddhists. Objects are interpretative imputations made by the observer. The so-called material substance is but a small part of all conditions, combination of which leads to arising of this particular delineation and designation.