Developers need to perform adequate testing to ensure the quality of Automatic Speech Recognition (ASR) systems. However, manually collecting required test cases is tedious and time-consuming. Our recent work proposes CrossASR, a differential testing method for ASR systems. This method first utilizes Text-to-Speech (TTS) to generate audios from texts automatically and then feed these audios into different ASR systems for cross-referencing to uncover failed test cases. It also leverages a failure estimator to find failing test cases more efficiently. Such a method is inherently self-improvable: the performance can increase by leveraging more advanced TTS and ASR systems. So, in this accompanying tool demo paper, we further engineer CrossASR and propose CrossASR++, an easy-to-use ASR testing tool that can be conveniently extended to incorporate different TTS and ASR systems, and failure estimators. We also make CrossASR++ chunk texts from a given corpus dynamically and enable the estimator to work in a more effective and flexible way. We demonstrate that the new features can help CrossASR++ discover more failed test cases. Using the same TTS and ASR systems, CrossASR++ can uncover $26.2%$ more failed test cases for 4 ASRs than the original tool. Moreover, by simply adding one more ASR for cross-referencing, we can increase the number of failed test cases uncovered for each of the 4 ASR systems by $25.07%$, $39.63%$, $20.95%$ and $8.17%$ respectively. We also extend CrossASR++ with 5 additional failure estimators. Compared to worst estimator, the best one can discover $10.41%$ more failed test cases within the same amount of time. The demo video for CrossASR++ can be viewed at https://youtu.be/ddRk-f0QV-g and the source code can be found at https://github.com/soarsmu/CrossASRplus.