Am I considered to be a materialistic person?

Strictly looking at it, yes you are materialistic. And doesn’t matter what you tell or don’t to her.
“Obsession with my equipment" is enough to answer your question. No need for endless tries to convince yourself or others about the contrary.
Finally a serious topic, not the shabby ss vs tubes.

Yes, as others have said. But at least it’s an obsession you can share with others. Almost everyone can listen with you and appreciate how great it makes their favorite artist sound. They may not understand the obsession but they can appreciate the stuff - at least for a while. 

Not all hobbies give you that!

I don't see the harm in being a little materialistic. Human nature. But, like anything else, it can be carried to extremes. A little of almost anything is fine. If it begins to hurt someone else, or disrupt your life and family, then its starts to be a bad thing. In my humble opinion.

Give me a tasty blonde, anytime! 

Three things, in no particular order, comprise my short list of obsessions: Long rides on my Harley; afternoon, late night, sometimes all night listening sessions of my favorite tunes and taking care of my large yard full of trees. I'm most grateful my wife is  patient with the Harley and music thing and greatly enjoys the trees, as it makes a great haven to accommodate her love of wild birds.
Maybe a bit materialistic, but it keeps us sane.......Jim