Tell boss that you need to skip this upgrade and wait for next.
Write a letter to vender management stating it didn't add values but cause signifant drawbacks. This upgrade is not for you. The sales failed to explain to you in sufficient details but stalked you for the purchase in software and training. You need to ask for the money back. If this letter doesn't work, you need to write to the CEO next.
you also need to Ask bank(or credit card company) how to reverse the payment. But I am afraid you will have to prepare for partial loss of this $6000. Worst case is to suit (as a company, you have to hire attorney, which is easily over $6,000).
Your supervisor also has joint mistake for authorizing this money without verifying. Maybe your company is too large to care.