Hi guys. Thanks for all your posts with knowledge regarding Klipsch rp600m upgrade. Thanks to #dtossan for posting the schematics. I decided to dig into and to built separate crossover with good parts and to add damp material for the internal of the cabinet.
For the damping I used 4mm CTK premium antivribrating mat, which is used often in car audio (this is where a bought it - in a car audio shop). After that the cabinets felt more heavy and more solid. I even put the material around the bass reflex tube. Then I added a "acoustilux", which is kinda similar as it was already inside by default, but this new one is more densed and it feels much better. It's made by Jantzen Denmark.
For the crossover I used a Jantzen air core coils, a Jantzen superior capacitor for the tweeter and a Clarity Cap CSA for bass driver. Oh and the internal wiring was with Jantzen copper/silver wire.
The total cost of the material was around 150 USD.
And the sound Well, I didn't expect too much, because I didn't want to be disapointed. But, it's quite a night and day difference. It's very pleasing to listen to them, more linear, more refined, bass is compact and punchier. They are in different league now for sure.
Best, Gasper