Our extension is not a typical luggage rack so the universal will not fit. If you are willing to drill the heck out of the stock rack it would be fine. With the SR92 it is much easier and more secure as now the universal plate is bolted to a metal base. For the wiring connection I also purchased the Bestem quick disconnect. It is more expensive than just a trailer disconnect but works well.
With any Givi box unfortunately you will ne either the SR92 or SR92M. The advantage of those box's is with the proper mount no drilling at all will be required. Expect to spend quite a bit more though. Adding the backrest pad and lighting can get even more expensive.
A side note is I finally used the custom internal LED lights last night. They are a great addition to the box. Well worth the effort and you do not mind epoxying light strips to a $100 box.