You are right, probably magic buckets should be the best for outdoor workouts so I’ll try that feature when I have bought the karoo.
Today I also got an answer from the hammerhead support to my question concerning the sounds: the karoo speaker cannot be accessed by extensions and other apps due to software limitiations of the karoo system. another way to avoid that problem is to download the workout as ZWO file to the device and play it from the karoo system.