For what it's worth, I just installed a Givi SR-19 Topcase Rack, Givi V46NT Topcase, and a Givi TB19 backrest on my 2006 Silverwing. I got them from Twisted Throttle which provided very good service. The prices were very good and they delivered on time so I can recommend them. The only drawback was the documentation Givi provides. It is simply a parts blowup of each unit with no instructions on the sequences for installing each unit. Needless to say, I "re-installed" them several times.
However, now that they are installed and have not fallen off during several test rides, I am very happy with the quality and functionality they provide. My wife especially likes the backrest...............Happy, safe riding. Jack

I share your liking of them - I used the pictorail on here - it doesn't show the back-rest but the pictures make it obvious how it fits with the rack.