Believe Redrumloa had the Sonnet Encore g4 card on his Quicksilver Mac a few years ago. Mind you that MorphOS will only use one of these CPUs and not both. :)

But if you have the that card, throw it in! :)

****Just be sure you've done any firmware upgrading to the quicksilver if you need. You may have to google it. I know I had to flash a MDD mac before I installed a Sonnet card into the MDD. May be the same story for the Quicksilver.