mix using 3model GPU mining issue (Nvidia and AMD together)

New here, New miner, just build a new mining system. will list hardware as follow
MB: Asus z97-a
CPU: i5 4570
RAM 2x4G DDR3 1600
SSD: Kingston 250G
PSU: corsair TX750M
GPU: 2x msi Radeon RX 6800 gaming x trio 16G
1x MSI VENTUS 2X OC GeForce RTX 3070 8GB

here is the issue.
When I put the first 6800 on the system, no issue. mining by nicehash the rate is around 58
and I add second 6800, no issue, mining rate 58*2
BUT, when I add 3070, unusual things happen, only one 6800 working properly, (rate=58)
the 3070 also working and the rate was around 56, But there is one 6800 was recognized but not mine. (driver success,)
I believe maybe the slot wrong, so I swap the GPU 3070 with the unusual 6800, still the same issue.
I took out the 6800 which was working fine, leave 3070 and the unusual 6800, all is fine.
I believe maybe 2 reasons
1.The power supply output not enough
2, The motherboard BIOS need to be setup.(only 2 cards at a time?? or PCIE version?)

Now I am ordering another PSU (on the way)
Just wanna ask if the BIOS needs to be configured in some proper way?
Thanks in advance.