My current theory (note: I really don't want this to be true, but I have a bad feeling about some of the 'previously' scenes, and RTD's reluctance to use older continuity):

Adam is behind the new Dalek fleet. After the Doctor returned him to 2012, Adam still retained all the information that he downloaded from Space Station 5. Given that SS5 was in the planet's far future, it's quite feasible that the station contained information about the Daleks from other incursions (such as those in Remembrance and the invasion of the 22nd century). Using this, plus what he learnt from his time with van Statten, he turned himself into a proto-Dalek, making him immortal. He then hides out on Earth for the next 200,000 years, possibly in the Utah compound. When the news channels of Space Station 5 crash, he takes advantage of the confusion to buy SS5 (after 200,000 years and knowing how the stock market will turn out, I'm sure he could raise the funds). He converts it to The Gamestation, picking people off Earth at random. The losing contestants are not killed, but instead turned into Daleks. After 100 years, 400,000 people have been converted into Dalek soldiers.

Problems? Well, it doesn't explain Bad Wolf. Rose is told during The Unquiet Dead that she's met the Bad Wolf already, but that's before she meets Adam. Secondly, sure, Adam might be angry at being left on Earth, but enough to create a whole new race of Daleks? Seems a bit odd. But the more I think about it, the more I'm convinced that the voice belongs to him…

(still think it'd be great if it was Paul McGann though)