Not sure about the Eheim filters, but if you only interest in adding an additional filter or improved flow you could just add a pump inline with the outflow of the Filter to improve the the flow from the filter.

I've done this with my Rena XP4. I found the flow deplorable so I added a MagDrive 9.5 and the flow easily tripled. I've found no adverse effects to the biological. Its cheaper than buying another filter just to add flow and it pretty much ensures that your top draw canister will never airlock on you.