The radio group is expected to appoint an advertising agency to work on the two brands once a marketing strategy has been finalised.
Graham Bryce, the managing director of Xfm and Choice, said: "We will be looking at the people who work with us. Whether we'll look to use something new has not been decided yet but we're not opening up a pitch."
Rocket currently handles media strategy for Xfm but Capital may need to appoint a creative agency to handle above-the-line advertising. Delaney Lund Knox Warren & Partners handles the 95.8 Capital FM brand.
The increased investment is likely to be split between above-the-line ads for Xfm and product improvements and trade marketing for Choice FM, the London urban station that Capital bought six months ago.
Bryce said: "Capital has a strategy of building complementary brands in the marketplace. It wants to create four strong brands but the ad recession meant that there weren't necessarily funds to invest in them all."