Im more interested in the talking darkspawn. Are they the original magisters of old? Descendants?
courtesy of the legacy dlc we know at least one was a tevinter magister.
Corypheus was a Tevinter Magister, but I don't think that Architect was. Architect cannot control the taint in a way Corypheus can - he was able to make sentient Darkspawn and was able to accelerate spreading of the taint in Grey Wardens (The Calling), but by no means was he able to directly control anybody. Even his influence on other, non-sentient darkspawn was very limited.
There is one more thing. Architect clearly feels kinship with the darkspawn, and his ideas are meant to benefit his kind. He is also willing to kill the Old Gods, while Corypheus seems to be a faithful servant to Dumat - unaware that his god is dead.
He notices that Dumat is not responding and says "Dumat, have you forsaken me? I am your faithful servant...".
This means, that the Old Gods were able to actually communicate with people. However, now they are only able to communicate with those who are tainted (the darspawn and old Grey Wardens).
Now - a speculation of mine. I don't think, that darkspawn taint the Old God when they find one in the deep roads. I think that they just release him, and the Old God is already tainted. All of the Old Gods became Archdemons after the Magisters visited the Golden City. That's why they can only communicate with the darkspawn - while before they were able to communicate and call to regular believers/their priets/Magisters.
That's why they force the darkspawn to dig in search of them - they want to be released and they want a Blight.
The one question that troubles me, is why Corypheus can affect the tainted in a similar manner to the Archdemon?
Anyone remember what old corypheus says? That the golden city was already dark when they arrived?
So they were offered power, corrupted by this darkness, and through them the taint was spread to thedas it would seem.
Corypheus said (direct quote):
"The City! It was supposed to be golden! It was supposed to be ours!"
Meaning that the City was already tainted - or at least Corypheus thinks it was. The Chant of Light says:
"And so is the Golden City blackened , with each step you take in my Hall
Marvel at perfection - for it is fleeting.
You have brought Sin to Heaven and doom upon all the world"
Which means, that according to the Chantry, the Golden City became black while the Magisters entered it, and the description suggests that it was a slow, continous process, because the Magisters had the time to "marvel at it's perfection". Accoriding to Corypheus it's not true - the City was already black, or became black immediately after they reached it.