After a difficult and expensive 17-month struggle to gain the Federal Communications Commission’s approval of their July 29 merger, satellite radio companies Sirius and XM — and their hard-charging CEO Mel Karmazin — now must take on even bigger challenges: Integrate the two companies, stanch the flow of red ink and compete against traditional radio as well as Apple’s iPod and other entertainment choices. The FCC took its time approving the Sirius-XM merger partially because the deal created a monopoly in satellite radio. Sirius and Karmazin argued successfully that the acquisition of XM should be approved because the companies compete in a larger market for audio entertainment that is ruled by the iPod and traditional radio stations.…