DDR5 6000 MT/s at dual channel = 96000 MiB/s or 93.75 GiB/s theoretical maximum memory bandwidth / speed. [ 3000 MHz DRAM clock speed * 2 (for double data rate or DDR) * 8 byte wide bus width (IMC to DRAM bus on x86-64 architecture) * 2 (if you're running dual channel) = 96000 MiB/s ]

Your DDR5-6000 setup brings read speed at ~83.45% and write at ~89.8% speed of the maximum possible bandwidth. Generally the effective (practical) speed should be close to around 92% to 98% of the 93.75 GiB/s, if not pretty close. But it isn't. Basically, the actual write speed of your setup is close to DDR5-5400 and read is close to DDR5-5000. It means there isn't any reason to run at DDR5-6000 if you're not getting any extra bandwidth over lower speed or significant latency improvement. I'm not familiar with Zen based systems, but it looks like there is bottleneck somewhere, either the IMC is not fast enough, or the cores of Zen 4 aren't fast enough for that DRAM speed, or may be the Aida64 has got some problem with Zen 4.

4 DIMMs will always lose performance versus 2 on a dual channel system, it's a consequence of the IMC needing to handle multiple signals with different trace lengths (due to daisy chain). Particularly since these are 32gb DIMMs, ie dual-rank.