https://www.reuters.com/article/us-s4-capital-deal/sorrells-s4-capital-content-arm-buys-firewood-ad-agency-in-digital-push-idUSKBN1WN0J6 >S4 Capital's content unit, MediaMonks, is set to merge with Silicon Valley's biggest independent agency, Firewood, as the Martin Sorrell advertising vehicle ramps up its digital push and raises funds to expand.