Asuri,
"There are a few billion Hindus and Buddhists who would disagree with Amir’s statement. You do not hear them chanting “Amir” or “Fred”. "
Even if the whole world had done it, that does not mean the whole world is correct. In the Way, it is not a matter of strength with numbers or conforming to a certain pattern of thinking. While there are many working towards the Way, very few ever come to it’s realization simply because they are far too entangled in their own discipline, clinging to their belief systems, religions, and philosophies. And being part of a tradition, before you even enter into the search for Truth, your mind has already become prejudiced.
Yes, any symbol which represents the divine can be used as a means towards one’s enlightenment, concentration upon “Om” is not the only method. For the Hindu, it may be Shiva or Krishna, for the Zen disciple it may be word “Mu” - which is the essence of the whole training of Zen, for the Pure Land Buddhist it is the Nembutsu - the name of Amitabha Buddha, for the Sufi it may be Allah, for the Qabalist it may be the divine name Eheieh (I am), which is the highest divine name in their system, and you can go on and on finding as many different approaches towards the same phenomenon. And that is just with mantra yoga, one is not considering any of the other approaches. In bakhti yoga, again, any object of devotion will do - it does not have to be the symbol “Om”.
“It signifies or symbolizes or expresses something very specific, and has a particular resonance.”
It does. But it is not the only approach.
“The yantras and tantric deities used for visualization also have specific meanings.”
They will mean whatever one wants them to mean, they are just a skillful means. In Tibet, you will not find a shadow of any of the Hindu deities left, and their methods work perfectly well. Whether you are using a deity of some particular tradition is not the essential phenomenon. You can even invent your own, and in fact in tantra there is a whole science as to how to create your own thought and energy forms which can function independently of one’s own consciousness.
“They are not a substitute for “Om”.”
They can be.
“Likewise, the imaginations of our own mind are not a substitute for real knowledge.”
Knowledge by it’s very nature is relative. And the moment you cling to knowledge as though it were the ultimate, you are already suffering from your own hallucinations.