Aaron has decided to use the audio recording modeling strategy from a single-subject study with his client who also has struggles with initial word sounds. the type of replication that aaron illustrates in this case is:

Systematic replication.

Explanation:

By definition Systematic replication is "a way to increase the generality of an experimental finding by conducting other experiments in which the procedures are different from the original research but they are logically related".

And on this case that type of replication describe the situation perfect since Aaron is interested in order to analyze if the subject present problems with the initial word sounds. And on this case this experiment can be generalized if we have a lot of replications in order to ensure replicability.