if you had this system, what would you do to make it sound the best you can

Riccitone advised you well...

upgrading is not recommended as a first move if your system is already synergetical...

To go for more learn about your electrical grid, the control of vibration on your system and room acoustic...

Upgrading will give you no knowledge at all save if some gear piece is too much sub par to the other piece ...

You must learn with what you have and then after exploring the way to use optimally what you had already then you will know what piece3 to upgrade and why ...

The most fun part of this hobby is the journey in experimenting with what you have already ...

upgrading will never be so gratifying than creativity...

Upgrade is useful when we know why with what and how to install it rightfully in a room with the other pieces...

Takes your time read a bit and think with simple experiments to begin ...

I bought new Quad ESL's 15 years ago - and I'm keeping them. The 29 series is very smooth and elegant, and build quality is high. The 28 series is brighter, too bright for my taste. YMMV

What are your ears missing?  What do you want to hear more of.  What kind of music do you listen to?

Remarkably, no one's touched on the elephant in the room:  You've got all this McIntosh gear and are using a low-fi piece of junk ADC equalizer.  First thing I would do is ditch it.  You will find that the system suddenly sounds more open, with better dynamics, lower noise, and less graininess.

I’d agree with @jhnnrrs about the equalizer you have in the chain.  I’m not sure why you would need it given you have an 8 band in the preamp.  Pull that thing out and get yourself a nice external DAC.  Not sure how much of your listening is digital vice vinyl but an external DAC would likely make a huge difference depending on budget.  You could likely do better for speakers given the level of your other components but I’ve never heard the Spendors.