General Instrument Corp., the largest manufacturer of cable TV set-top boxes, confirmed board member Daniel F. Akerson as chairman and chief executive, effective Aug. 28. He replaces Donald Rumsfeld, who will remain as a director.Akerson is president and chief operating officer of MCI Communications Corp. EMI Music is acquiring a stake in Musicom Intl., a dealer of high-end rock music memorabilia. EMI, one of the world’s largest music companies, intends to invest $ 1 million in Musicom for a 10% share, plus lend $ 4 million more. The loan would be convertible into an additional 41% of the shares, and EMI can up its stake to 80%. After April 1, 1996, the remaining 20% could be acquired. Hughes-AVICOM Intl. has received a $ 19 million order from Virgin Atlantic Airways to equip the airline’s seats with hardware to carry Nintendo videogames and other in-flight services. The GM/Hughes Electronics Corp. subsid expects to have the units installed in every seat of Virgin’s 11-plane fleet by the end of 1994. Children’s Broadcasting Corp. of Minneapolis reached a preliminary agreement to buy Orange County Broadcasting Corp., which operates L.A. radio station KPLS-AM. Terms were not disclosed. Deal is contingent on definitive merger agreement and FCC approval.