I own 1968 Series 1's. Even if the OP has Series 6's which don't I have experience with. Just get a minDSP from Amazon for $125 (100% money back) and dial in the curve for the Series 5 or 6. If the OP likes what he hears. Awesome !
I run Klipsch Cornwall IV's with a 500WPC GaN FET Amplifier and swap in the 901's on occasion for fun. They are great Speakers for what they do. No, you can't hear the fart of a Nat like I can with the CW4's. But I still enjoy what they. No foam rot either cause the Series 1's and 2's (which I also own) are cloth doped surrounds. If the OP's Series 6's are the V2 with the "rolly" surrounds. Foam rot shouldn't be a problem.