1. A method of multi-stage entropy coding of symbols using a computing device that implements an audio encoder, the method comprising: receiving plural symbols, each of the plural symbols having one of M possible symbol values; with the computing device that implements the audio encoder, for the plural symbols, selecting an entropy model from among multiple entropy models of a first model set a plurality of the multiple entropy models of the first model set including a model switch point for switching to a second model set that includes a single entropy model, the first model set further including at least one entropy model that lacks the model switch point for switching to the second model set, wherein: each of the multiple entropy models of the first model set is associated with a different distribution of the M possible symbol values; and for a subset of plural less probable symbol values among the M possible symbol values, the single entropy model of the second model set is associated with a common conditional distribution of the plural less probable symbol values across the different distributions for the plurality of multiple entropy models of the first model set that include the model switch point; with the computing device that implements the audio encoder, for each single symbol of the plural symbols, using the selected entropy model of the first model set in first-stage entropy encoding and selectively using the single entropy model of the second model set in second-stage entropy encoding to entropy encode the single symbol; and from the computing device that implements the audio encoder, outputting results of the entropy encoding in a bit stream.