Presentations on public information systems, like a large screen in a museum, usually cannot support heterogeneous user groups appropriately, since they offer just a single channel of information. In order to support these groups with mixed interests, a more complex presentation method needs to be used. The method proposed in this paper combines a large stationary presentation system with several Personal Digital Assistants (PDAs), one for each user. The basic idea is to ”overwrite” presentation parts on the large screen, which are of little interest to a particular user, with a personalized presentation on the PDA. We performed an empirical study with adult participants to examine the overall performance of such a system (i.e. How well is the information delivered to the users and how high is the impact of the cognitive load?). The results show, that after an initial phase of getting used to the new presentation method, subjects' performance during parallel presentations was on par with performance during standard presentations. A crucial moment within these presentations is whenever the user needs to switch his attentional focus from one device to another. We compared two different methods to warn the user of an upcoming device switch (a virtual character ”jumping” from one device to another and an animated symbol) with a version, where we did not warn the users at all. Objective measures did not favour either method. However, subjective measures show a clear preference for the character version.