Crosscutting concerns are an intrinsic problem of legacy systems, hindering their maintenance and evolution. A possible solution is to modernize these systems employing aspect-orientation, which provides suitable abstractions for modularizing these kind of concerns. Architecture-Driven Modernization is a more specific kind of software reengineering focused on employing standard metamodels along the whole process, promoting interoperability and reusability across different tools/vendors. Its main metamodel is the Knowledge Discovery Metamodel (KDM), which is able to represent a significant amount of system details. However, up to this moment, there is no extension of this metamodel for aspect-orientation, preventing software engineers from conducting Aspect-Oriented Modernizations. Therefore, in this paper we present our experience on creating a heavyweight and a lightweight extension of KDM for aspect-orientation. We conducted two evaluations. The first one showed all aspect-oriented concepts were represented in both extensions. The second one was a experiment, in which we have analyzed the productivity of software engineers using both extensions. The results showed that the heavyweight extension propitiate a more productive environment in terms of time and number of errors when compared to the lightweight one.