Current methods for immersive playback of spatial sound content aim at flexibility in terms of encoding and decoding, abstracting the two from the recording or playback setup. Ambisonics constitutes such a method, that is however signal-independent, and at low spatial resolutions fails to provide appropriate spatialization cues to the listener, with potential severe colouration effects and localization ambiguity. We present a new signal-dependent method for parametric analysis and synthesis of ambisonic sound scenes that takes advantage of the flexibility of Ambisonics as a spatial audio format, while improving reproduction. The proposed approach considers a more general acoustic model than previous proposals, with multiple source signals and a non isotropic ambient component. According to a listening test using headphones, the method is perceived closer to binaural reference sound scenes than ambisonic playback.