Strip wash with washing up liquid? I've only heard about it (done lots of research, 6 months pg with dc1), but i think you do a pre-wash, wash at 60 with a tiny bit of washing up liquid, then keep running rinse cycles until there are no more bubbles
Not sure if you can do it on AIOs, but Google is your friend
Deff give them a good stripping. You say you prewash is that hot or cold? You need to do cold before the main wash to avoid setting in the smell. I jsut do a rinse then put them on a 60 quick wash and I use ecoballs for the nappies so never get a detergent build up.