You're going to encounter some problems:
3x2 3,840 x 2,160 is 11,520 x 4,320, do depending on who you ask, 11/12k or 4320p, also 2.66(6) ratio, so even more than cinematic 2.35:1.
To get 8k from 4k screens you need 2x2 set, to make 24k you'd need 6x6 set, so 36 screens.
Returning to what you've come up at, even 2080ti has HDMI 2.0b(14.4 Gbit/s data rate) which caps out at 4k 60Hz without HDR, 4k 50Hz with HDR or 4k 60Hz 4:2:0 with HDR, I think this is the reason for the 4k cap you encounter. DisplayPort1.3 is more capable( 25.92 Gbit/s data rate), but only barely. Your config is basically 1.5 times the pixels 8k screen has, which would need ~75 Gbit/s at 60Hz(or 90 with HDR). DisplayPort2.0 might be of help here with 77Gbit peak data rate and Dispaly Stream Compression(1.4 also has DSC, so there's room to fiddle)
With DP 1.3/1.4 half the res you have (5,760x2,160) should be doable, but I doubt anyone has a solution like that, the aforementioned walls will be the only feasible thing for a year or two I'd think and I wouldn't bet on DP 2.0 making a difference either.