Hi pima~,
Firstly, you are running an AMD processor which are unsupported unfortunately as they have known issues with live streaming audio applications. This could be related to why you are getting such bad performance in current versions of ITCH. You are also sitting just above the minimum required specs to run ITCH, it could be that because the older versions are less CPU heavy that you have been running into less problems.
Having said that, since you have had no problems using 1.6 there might be some troubleshooting we could do to try and get 2.1 working for you.
Could you please perform a RATT report and upload the results to the thread? You can find instructions on how to do this here:
serato.com
Can you also let me know if you change the buffer size in the setup screen if it has any effect?
Sam.