currently using one, bought it thinking i could connect 19 Vega64 on it but allas it can only BARELY support 8 of them
i have 6 on it and its stable but no more
That is an issue with the drivers for the Vega, not the motherboard - EVERYONE has been having issues getting more than about 4 Vega cards working on one rig, and I've NEVER seen a "working on more than 6 reliably" report.
With that said, the weird no-reason-for-it limitation to 13 "non-mining cards" has never been explained by ASUS, and there is NO sensible reason for it.
They've also never specified if anything OTHER THAN the P106 mining cards count as "mining cards" or WHY they have the restriction in the BIOS or what the BIOS is looking for when it imposes that senseless restriction.