Upgrade

As your current system seems well done I will assume your acoustic treatments are also well done.

I tend to think I'd sell the older ML amp and shop for a 6-12 month
old, one owner Pass Labs XA25. Can be had for $3k.

That will give you the low end slam you want as well as better
overall experience. 

You already have the tube preamp so good synergy with SS Class A
amp.

My 2 cents worth.

Please keep us posted on your results.

Isolators under your ARC, I have Nimbus under my REF5se...

arrange to borrow an HRS Turntable platform

Thank you all!!
I will try different power cords, IC’s and isolators first, before changing any of the other components. Thanks again for all your suggestions

bms72, sorry that I am late to the game. You have a nice system. Power cords and isolators are not going to do much. But what will make a significant difference is a new tonearm. I believe you have a unipivot arm on that turntable. Unipivot arms have to many degrees of freedom, they are floppy and hard to keep perfectly aligned. Several cartridge manufacturers such as Lyra recommend against using them. They are particularly bad with medium to low compliance moving coil cartridges such as yours. Moving to an arm with fixed bearings will for certain improve bass and dynamics and may well improve other areas. Look at Origin Live, Kuzma, Reed and many others. VPI also now makes an arm with gimbal  pivots which might be a direct replacement. 

Thanks mijostin. I am certainly not an expert when it comes to tonarms... but I m actually pretty satisfied with the bass and dynamics in my system. My current MC cartridge is a Dynavector 20x2H (high output). 

I am looking for a larger more open soundstage, more liquid, but without loosing the punch. The ML 23.5 does pretty well with my Graham speakers, even though they only go down to 40hz.