EMA C++ Configuration Guide : 3 Configuration Groups : 3.3 NiProvider Group : 3.3.2 Setting a Default NiProvider
 
3.3.2 Setting a Default NiProvider
If a DefaultNiProvider is not specified, then the Enterprise Message API uses the first Provider component in the NiProviderGroup. However, you can specify a default provider by including the following parameter on a unique line inside the NiProviderGroup but outside the NiProviderList.
 
 
<DefaultNiProvider value="VALUE"/>