The motives behind the takeover are the easy bit: Profit.
Simple as that. They obviously believe they can make a profit out of owning NUFC, the real question is: how?
There are a number of ways they could attempt to do it, some reasonable, some not.
Basically I think their approach will depend largely upon how quickly they want to realise the profit.
If they're looking for a quick buck then I think they'll try to get the club moving in the right direction and take the profit from the resulting share price increase. This could mean the club changes hands again very quickly, after as little as a couple of years maybe.
If however they're in it for the long haul, then, as Parky says, the money is generated through using the club as a marketing tool. Basically you stick the club logo, etc, on any prduct you can think of, add a premium to the price and take your 10%. Man Utd are the only club to do this even remotely successfully at the moment, there's potential for other clubs to do the same or more even. They have their name on loads of stuff, from toothpicks to financial products, there's even a "Red" cinema, which brings me nicely on to the best example of how much money can be made through effective marketing, films.
Hollywood is the prime example of the kind of money football could be bringing in and it's the reason why people are still prepared to invest significant amounts of money in what appear to be loss making businesses (Football clubs). Hollywood films make most of their money through marketing/merchandising, I don't have the figures, but I'd be willing to bet that the cash brought in by marketing dwarfs ticket sales for almost all modern hollywood films. Often the film itself is almost an afterthought to the merchandise nowadays, the studios know that they don't even have to make a very good film to make a profit. If they do manage to end up with a commercially successful film, then it's megabucks time!! This is why we have to put up with things like: Dude Where's My Moped 89 and Gone in 60 Seconds 33 - Wolverhampton Wheelie, because once one of these franchises has made it big they can produce endless sequels and spinoffs, and it doesn't even matter if no-one goes to see it, because the marketing brings the money in anyway. Did you know that Waterworld, widely considered the biggest box-office flop of all time, actually made a healthy profit when the marketing income is taken into consideration?
Investors continue to believe that similar things are possible using football, no-one's really done it yet, but they still think they will, who knows they might be right, lets hope it's us who makes the breakthrough.