You can turn DimPro into a multi-timbral instrument (up to four parts) by clicking the second button in the group of four buttons at the top center of the application. When in multitimbral mode each element is on a different MIDI channel (Element 1 on channel 1, Element 2 on channel 2, Element 3 on channel 3, and Element 4 on channel 4). With multitimbral mode enabled you can then have one DimPro instance receiving MIDI data from four different MIDI tracks each sending on their own channel.
But multitimbral mode not the normal mode of operation and could cause issues if you want to run four parts but some of the patches you want to use are multi-element patches.
You should be able to run numerous instances of Dimension Pro without crashes. Makes me wonder if there is something wrong with the particular drum patch you're wanting to use. Try using a variety of different patches and see if they all do the same thing.