Hmm. This is weird. Just reinstalled Win10 fresh, removed compiled kernels and launched the SRBMiner but now it reports both cards as Vega 
This is Vega 56 + RX580 setup. Even used DDU to remove stock drivers before installing latests.
Even compiled kernel files looks like this https://i.imgur.com/n1IJgwp.jpg
EDIT: Even more weird. I can only see RX580 with HWiNFO.
EDIT2: Forgot to put Compute mode on for RX580. Haven't tried without it so didn't know it would work like that in graphics mode.
EDIT3: After I rebooted, both showed up as Vega again even in this compute mode but this time speeds are decent and I can see both in HWiNFO. Re-ticking Compute mode makes them both get recognized again.
Quote
GPU0: Radeon RX Vega [Ellesmere] [8192 MB][Intensity 52.0][W: 8][T: 2][K: 1][BUS: 6]
GPU1: Radeon RX Vega [gfx900] [8176 MB][Intensity 111.0][W: 16][T: 2][K: 1][BUS: 11]
GPU1: Radeon RX Vega [gfx900] [8176 MB][Intensity 111.0][W: 16][T: 2][K: 1][BUS: 11]
This is Vega 56 + RX580 setup. Even used DDU to remove stock drivers before installing latests.
Even compiled kernel files looks like this https://i.imgur.com/n1IJgwp.jpg
EDIT: Even more weird. I can only see RX580 with HWiNFO.
EDIT2: Forgot to put Compute mode on for RX580. Haven't tried without it so didn't know it would work like that in graphics mode.
EDIT3: After I rebooted, both showed up as Vega again even in this compute mode but this time speeds are decent and I can see both in HWiNFO. Re-ticking Compute mode makes them both get recognized again.