Agreed. You are wasting your time trying to polish them, they will look awful if you try with any kind of abrasive or strong solvent.
If you have a really bad mark on them, i'd suggest re-casing by your local B&O engineer/dealer. Otherwise - leave well alone.
Sorry if this isn't what you want to hear, but theres nothing worse than having the best intentions and ruining your B&O. On his first day, Matt (LifeStyle AV) cleaned a mark off the front of a Beolab 2000 with thinners!! Of course, it melted the grey plastic, but thankfully i laughed and counted it as a valuable lesson in being very careful with B&O.
He has since gone on to be a star employee by the way.
Lee
BeoWorld - Everything Bang & Olufsen