Would saying "ve-dibarta BAM!!!" (with the letter A pronounced like Apple) help me to discharge my obligation when reciting kriat shema, or would it be better that I say "bam" instead? (the letter A pronunced like stackexchange.cOm)
Your question is a little confusing: are you asking about stress or about vowel quality? So far as stress is concerned, the phrase is pronounced vedibarTA BAM, with a stress on the final syllable of the first word and on the second word as well. (This differentiates it from vediBARta BAM, which would be a perfective: "and you spoke of these things".)
So far as vowel quality is concerned, there are different traditions. Given that the word is written (in Deuteronomy 6:7) with a qamatz, many Ashkenazim would pronounce it like the O-vowel in "drop" (Australian English pronunciation), while many Sephardim would pronounce it like the A-vowel in "rum" (AustlE again). Even if you are Ashkenazi, you might prefer to pronounce it with the Sephardi pronounciation, given that this is the standard pronounciation in the State of Israel.
Finally, the mishna in Berakhot 2:3 states that you have not fulfilled your obligation in reciting the Shema unless you are precise about the letters (דקדק באותיותיה), and different commentators interpret this differently. Some (like Melekhet Shlomo), think it refers to aspirating non-aspirated consonants (and vice versa) or to running letters together, while others (like Rav Ovadiah of Bertinoro) think it refers to running two words together as one. Both of these interpretations are combined in the Shulchan Arukh (Orach Chayim 61).
At the end of the day, while most authorities think that you need to be careful about the consonants (or at least consistent with them), I don't think anybody worries about the vowels. Consider what Rabbi Moshe Isserles says, on Orach Chayim 61:24. Where the mechaber states that one needs to read the Shema according to the way in which it is vocalised in the Torah, he notes that "in these lands [ie: in Europe], people don't do this, but those who are precise with the language might be strict in this matter" (אבל לא נהגו כן במדינות אלו. ומכל מקום המדקדקים מחמירים בכך).
Finally, even the mechaber concedes (Orach Chayim 62:1) that while it is a mitzvah to be precise about the words, you have still fulfilled your obligation even if you were not.
I learnt from a classic textbook on Hebrew grammar by Weingreen that a patah carries the sound 'a' as in 'had', and kamatz gadol/kamatz katan are 'a' as in 'are' and 'o' as in 'hop' (I actually think Weingreen said 'oh' as in 'hope', which might explain why Americans say Moe-she and Aha-rone?!).
In any case I recently came across a fascinating piece in Conversations, a collection of essays put out I think quarterly by www.jewishideas.org. The piece in questions describes three sets of vowel-sounding styles. One with 5 vowels (I think Alexandrian/Egyptian/Southern Israel), 6 (Babylonian), and 7 (Yavneh, Israel or thereabouts - the edition of Conversations is not currently with me).
Styles where kamatz and patach are the same sound 'Are', where seghol and tzeirei are not distinguished - it is fascinating, and opened my eyes, frankly. See if you can get your hands on a copy of the current edition - issue 13: insights from the Sephardic experience.