Let's separate Recording from Mixing.
Your Mic Pre's are for recording, I understand that you like you Mic Pres, I also like mine and I need them, but for recording.
Your question is related to Mixing
What are some rack gear that you own you couldn’t live without on your mixes?
None.
I can't live without my Computer, DAW, Plugins , Sound interface, Studio monitors and headphones.
Don't need anything else.
I used so many rack gear over time, mostly all the know great stuff.
I don't need or miss any of it.
What in particular do you use them on that you feel make your mixes “perfect”.
It's not related to gear, even if you don't believe in it at this point.
It's much much harder than bying a piece of gear.
It has to do with your experience and your Brain.
You listen with your Brain, you make decisions with your brain, you are creative using your brain.
Your Brain is the most important piece of equipment in mixing.
Achieving a Brain capable of doing great mixes is hard, takes a long time, but doable although a lot of people are never able to achieve it even though they spent a huge amount of money in rack gear.
What benefit an expensive compressor or equalizer gives you if you don't know how do you want the kick Drum to sound for that particular song?
What god any rack equipment do if you don't understand the arrangement and don't know how to interpret musically the elements of the song?
Mixing is not about rack gear is about making different instruments work in a song, is about emotion, it's about getting the most potential out of the sound.
Someone that is able to achieve a perfect mix with rack gear is also able to achieve it with a DAW and plugins. It doesn't matter it's much more than that.
Best Regards