Sounds like you've got your system dialed in to your taste.
I've had a pair of ML ethos for 7 years with no problems and love the way they provide large sound but being semi-transparent up to don't dominate the room the way other floor standers do.
If it was me, I'd stick with what you have and or trade up to a newer ML speaker. If you feel the urge to play with the system, try a different pre-amp or set of interconnects for fun.
I've had a pair of ML ethos for 7 years with no problems and love the way they provide large sound but being semi-transparent up to don't dominate the room the way other floor standers do.
If it was me, I'd stick with what you have and or trade up to a newer ML speaker. If you feel the urge to play with the system, try a different pre-amp or set of interconnects for fun.