You're pretty much correct. However I wouldn't mix the two oils even though they are probably compatible. I would use up as much as the XPS as you can and drain the rest. Then add the quicksilver. In the meantime take about 1 oz. of each oil and mix them, if after about one day they are still mixed and don't gel it will be O.K.
BTW, jagilbert the brand of oil is not so important but the certification is, SeaDoo 2-stroke use API-TC certified injector oil, motors without RAVE valves can use either mineral or synthetic blend. There's a bunch of threads on the subject.
Lou