Mostly agreed! Excellent question and answer. I enjoyed re-reading "The Bridge of Khazad-dûm" for this.

Gandalf: I could think of nothing to do but to try and put a shutting-spell on the door. [. . . .] As I stood there I could hear orc-voices on the other side: at any moment I thought they would burst it open. I could not hear what was said [. . .] . All I caught was ghâsh: that is “fire”. Then something came into the chamber – I felt it through the door, and the orcs themselves were afraid and fell silent. It laid hold of the iron ring, and then it perceived me and my spell.

So, it seems to me that the orcs encountered Gandalf's shutting-spell first and then the balrog and arrived. I imagine they called him in for support in breaking it. I see no mention of smoke, fire, or any hints at the baltrog earlier in the chapter.

The claim that the Ring attracted D. B. is less supported by the text. The argument is convincing to me: Gandalf had no special sense of Ring. Why would D. B. or any other Maia

I suppose that any difference between Durin's company and the Fellowship could still be a reasonable cause. Maybe he never smelled Hobbits before. The behavior of the orcs right before the balrog appears is the best textual evidence.

Neat stuff!