Sorry, why not "мы обсуждаем концерту"? :P
"обсуждать" takes the accusative case.
The accusative form of "концерт" is "концерт". For masculine and neuter inanimate nouns the accusative form is usually identical to the nominative form.
Does "Мы беседуем о концерте" give a different meaning?
to me it would sound something like "we are conversing about the concert"
If someone replied to me it would sound eccentric
Why does "мы говорим о концерте" not work? Is it too general?
Talking vs discussing
To me, talking about the concert and discussing the concert mean the same thing. There is a slight difference in formality.
Я не думаю что это предложение природно звучить на Англискоме
This is a very natural sentence in English.
Why is it not " концерте" ?
Because it's not saying "in the concert".
In my opinion мы is unnecessary, because form of the verb includes the subject of the sentence.