There are a lot of them out there.
If you're not familiar with them, then I would recommend an AudioControl processor. I have used the EQX, but the EQL is a good one also.
They are not too expensive, and very easy to install, and when you're ready to upgrade, you can usually sell them for a decent price.
The manual will walk you through the install and tuning process.
There are probably more, but that is the easiest one I've used.