Sure, I'll take the bait....
Not only would it be interesting to learn how people use a DAW for this but if they even bother or need to do this. After all, if the rear chs are a bit loud, just grab the remote & dial them down a bit.
For myself this kind of manipulation is a middle step & depends what I start out with & what I want to end up doing. If I'm doling stereo to surround on the PC I am not a purist I will do whatever it takes to make it sound best on my system. Maybe not yours, just mine. AA 3 has 4 different types of EQ programs & they all fit different needs but I usually make curves on the 20 band. When start a project like this I begin with making the front chs sound good on their own & sometimes that includes the AA3 Pan/Expand effect to increase width. Many of the upmixes I make are from J Pop & that can sound strongly bright with thin bass so that's is easily adjusted. In a David Bowie Greatest Hits it seemed each song was either too bright or boomy so that took a bit of doing. After the front chs are tuned in Ilisten to the rear chs solo & see what needs to be changed there. Generally I will normalize front & back chs independantly to -1dB & then evaluate together & if they don't balance (usually the rears are louder) I will adjust till it all seems to be balanced. If matching to video I will do dts to go with the mpg but if strictly audio it would be multi-ch FLAC.
As you know I am fond of pre-synth & before my SMv2/Chase RLC-1 combo I would do that in 2 ch mode on the PC. Usually stereo decoded QS or DPL II will have a stronger front end & I adjust the pre-synth to the right amount to bring it into balance & when you do that it has a nice wrap around effect.
If I am using a digital source I can just use my Anthem to change bass/treble/balance but an analog 5.1 signal say from Oppo or Surround Master is not processed digitally in the Anthem so I have only balance & of course volume to adjust. Going through the Chase RLC-1 to the SMv2 I can adjust bass/treble their & wrap around effect. Still it's not as precise as what you can do on the PC. A million times easier.
Interesting that we independently posted a similar music/frequency chart:
https://www.quadraphonicquad.com/forums/threads/smell-of-smoke.27687/#post-470149