Automated Testing Tools - Back End That's Not Unit Testing

I have a question regarding automated testing tools. I am a manual test engineer who for the past year or so has developed via C# a front end automated framework for testing one of our web based products (using Selenium).

I was recently given the task of researching tools for back end testing that's not unit testing. We have recently acquired another company and they currently unit test.

My boss wants me to try and find a tool that is a level above unit testing for testing the "logical blocks" of features. The plan is for our developers to create an API for our product and then plug in a third party tool for running automated tests on the product.

We do not have unit tests for our product as it goes straight from dev to the test dept (manual testing).

Is anyone aware of such a tool. I understand we could develop our own tool, but for the sake of time and money I have been asked to see if something already exists to give us a jump start on testing.

Thanks!

-A