The tip of the Winsor & Newton fineliners are quite hard actually and work pretty well. Although the tip does wear out after repeated use (before the pen runs out of ink), so might not be the most ideal pen for the job. Also, the servo I use with the AxiDraw is the default one it comes with and doesn't apply any added pressure on the page.
The Copic Multiliner might be a good option then. They are just great in my opinion (But I use them for traditional illustrations), although a bit pricey.
