I might be wrong.

I don't think it is a good ideal to let your parents show financial support for themselves. You invite your parents for the purpose of visiting and family reunion. It should be your responsibility for their traveling expense, living expense, insurance, etc. Their own financial documents should only demonstrate their ties in China.

Show your tax return, investment, bank statement, pay check stub, employer letter, anything that can clearly show you are able to support your parents' travel and live in US.

$3000 per month sounds pretty good to me. A lot of students have successfully invited their parents with income less than $2000 per month.

Good luck!