Much of the work on media multiplexity theory (MMT) is based on unestablished relationships, in which more channels are presumed to be indicative of higher relational closeness. But a different set of relational dynamics may be at play in preexisting acrimonious partnerships. In this article, we investigate the use of different modes of communication by high-conflict separated parents (media multiplexity), and map changes in modes of communication (modality switching). Qualitative data from 68 separated parents in Australia who reported chronic parental acrimony suggest that a considerable amount of modality switching occurred postseparation. Consistent with MMT, multiplexity was evident but the degree of multiplexity was not as clearly related with the degree of closeness in the co-parental relationship as would be otherwise predicted by MMT. Recent insights into more pernicious forms of family dynamics set an important challenge for communication theories to better account for ex-couple motivational complexities.