The audio is different on them. Some have ALC8XX and some have ALC12XX. The msi ones I saw all had the 800 level and the asus has the 1200 level. Also even then there are differences, as people said they had popping sounds with asrock boards, whereas reviews mentioned how great the audio is on the asus.If I'm not mistaken you have an Asus B450-i? If so, that's their mini-ITX board and if I recall it does have a very good VRM section that features power stages, with drivers, hi-side and lo-side FET's all integrated in one package, and is very cool running. They do that because mini-ITX is a dense packaged board that will run hot with CPU, GPU and VRM's all closely arranged and crammed into (usually tiny) cases that feature limited airflow. A mini-ITX build, done right, usually requires expert-level build skills. And even then frequently means buying hardware twice when something doesn't fit or work optimally.
At any rate, since it's packaged so densely it needs those superior (and expensive) VRM components just to perform as competently as discrete (and cheaper) components can on an m-ATX or ATX board in a normal case with normal airflow.
MSI's audio CODEC's are the same chipsets as those used on any other boards. If you have a strong need for superior audio you'll either have to buy an enthusiast-class full size ATX board OR, the smarter choice, a third-party audio card you can move with you to the next computer.
I am technically using a matx case if I keep an itx mobo because the only itx case I lied was the Nano S and it blocks a fan on gpus, so I was too scared to get it, even though I don't OC or use a gpu much.
I'm not sure what I am going to do now. The leaks were hilariously wrong. It was looking like the 3700x would be 100% better benches, where now it looks like the 3700x will only be close to even with the 9700k, which in turn is only barely over 10% faster than the 2700x.