I had the same question a little while back, try the link below. It may not answer all of your Q's but it's a start.

Dale

Here is a link that might be useful: Boysenberry pruning

Forget about how your roses grow. Boysenberry canes that fruited last year are goners now. Remove them immediately. It is common practice to remove them as soon as fruiting is finished. At this point, the sooner the better. There's always going to be a tangle, but you can minimize it by removing vines immediately after fruiting. Where I live the berry farm workers leave the new boysenberry or marionberry canes laying on the ground. When the older canes have finished fruiting, they are removed and the new vines are lifted off the ground, looped like garden hoses, and attached up on the support wires. Looks strange. I'm guessing it's not optimal but they don't have time to arrange them and spread them out.

...but it may be optimal for machine harvesting if you are referring to commercial fields rather than u-pick fields.

Nina, yes, cut all the fruited canes down to near the ground and leave the flower-budded canes alone. Try to do this before the newest canes emerge, so they will not be damaged during pruning (or just prune up higher than the new emerging canes).

The old fruited canes may have some new growth further along, but you will not get many or any berries from them, plus you have to draw the line somewhere or risk having a rat's nest of canes.