Your way is best. Definitely shouldn't be soaking MCNs. They're not the same as the old terries, which our mothers would soak. You might like to get your DH to read the care instructions on the MCNs, because soaking will ruin them.

My way is to put all the nappies and covers through a rinse cycle, then a wash cycle with some detergent. Sometimes I'll add other clothes or towels to the wash cycle. The covers don't get washed unless they have poo on them or are really starting to smell.