Hertsman, I'm finding no soot at all on my exhaust tips so the muck on yours is probably just regular crud. I'd try just washing them like any other mucky part of the car before touching them with an abrasive cleaner.
Probably to the horror of this section of the forum rarely touch the car in winter months aside from washing light lens which given how wet its been this year not done either.
So its thorough clean finished with a coat of collonite in Autumn and next time bucket comes out is first decent weekend day in Spring.
So not even looked closely at the Akrapovic tips to see if coked up, they just look dirty from afar but on your comment Watts I will maybe take a bucket of soapy suds to them and see if it is just does plain dirt?
Be a winner if it was, as the R tips became really difficult to keep in good shape and though always managed to get them decent looking from a standing view with plenty of elbow grease and autosol, on closer inspection there was some ingrained coking for life.
The TCR in the grey really hides the dirt well, imagine when get a bucket to it there be much more filth than seems.