You could add an analog gamma adjustment circuit after your DAC output, that may smooth out your gradients enough.

You could also use an op amp to change the output range of the DAC output so that the low and high map into the middle useful portion of the full voltage range you're using now

EDIT ...

I have a 1950's Heathkit vacuum tube-based oscilloscope that I restored (1 MHz bandwidth! 100 kHz sweep!), and a new Siglent SDS1204X-E (4 channel, 200 MHz). Love the Siglent.

I love the HeathKit too, but only use it for audio signals and when I need continuous X/Y inputs, as opposed to sampled.

It's a solid plane full of current, and there's a slot cut in it, so it may possibly act like a slot antenna. Ground isn't "zero", and voltages are all relative, a slot in a ground plane can be just as bad as a deliberate antenna. I think. It's all theory to me, I don't (intentionally) make ...

I think you lose a lot doing that, you no longer have a microstrip, and it might make a loop antenna. Could be wrong though.

Multi-digit displays would cycle through the digits, displaying one at a time, quickly. A single digit only has 8 LED's, so on an 8 bit bus it's not saving you anything. You could use a latch to set the segment values.

If you meant you wanted to drive 6 digits, not 6 segments, then yes you can ...

She used KiCad, it's free. They also partner with or own EasyEDA which I think offers PCB design software ?

Wow, that is expensive. My daughter printed a 7"x11" four layer PCB for $80 I believe at JLCPCB

It'd be kind of cool if it multiplexed A15-A8 with D15-D8 and A7-A0 with A31-A25. Full 32 bit address 16 bit data in PDIP-40!