Direct mining motherboards with no risers are the best, they are very close to how you will plug a Asic miner and never look back, I only do updates on hive OS with riserless motherboard, no reboots or downtime.
I love that Asrock H510 Pro BTC that I got some months ago,I have put 4 cards directly in it because the other cards I have in another rig and it runs perfectly,cards running cool even in an open air rig like the one I have but when having 6 cards in here a closed case is the best option or as a minimum you should have additional cooling for the cards which is the cheaper option.I strongly agree with riserless motherboards being really stable and without problems,at least I didn't encounter any so far and I am not even running Linux but Windows 10.