Aman ji
I think that concentrating on ones breathing, like using a Mantra (Waheguru or otherwise) is just a means to an end; but not the purpose of Meditation - though many Buddhists I know don't seem to have a clue what it is that they're supposed to be trying to do vis-a-vis establishing a Sound Meditational Practice.
In my mind, the objective is to learn to 'tune out' the Grosser Part (the part that, I believe, is 'generated' by our hard wired brain) of ones Conciousness, and to, thus, become more attuned with - more aware of, the Subtler Part of ones Conciousness (the part which I believe is 'generated' by the Clear Light, Soul, etc.); as it is only when you've become as fully aware of this truly subtle part of your 'Total Conciousness Experience' that you'll be able, as Guru Nanak so wisely pointed out, to truly appreciate Waheguru, Yaweh, the Great White Spirit, etc..
As I like to paraphrase Shakesphere: "A Clear Light Diety Entity by any other name......."
Waheguru exists - manifests? - in a sort of Formless Realm; just as Tibetan Buddhism teachs, and Sikhism (at least) doesn't reject; and so, I believe, does the Subtler Part of your own being.
It's the part of you that will take on the 'new' body - or not - when you die, your Book Of Life is Read, you're 'Karma Score' - or 'Karma Grade' - is assessed, and you're Dharma is thus determined.
Enough ABCs! I just thought I'd add that; as the breathing thing is just a tool to induce the trance state.....etc..
