How many presentations can be shared in a direct IX5000-to-IX5000 call?

On an IX-to-IX point-to-point conference, you can share up to two presentation streams – for example, one presentation content source and one whiteboard source.
If hosting a meeting locally with no videoconferencing, you can share up to three presentation streams.
Reference: http://www.cisco.com/c/en/us/td/docs/telepresence/ix_sw/8_x/admin/guide/ix_8_admin_guide/ix_sw_features.html