I am sure you would be pleased with either speaker. As I said in my earlier post I have listened to both although the Cantata was in 1979 when I purchased my KEF Calinda speakers. I still have the Calinda and also the 104/2. In my opinion (and of course everybody hears things differently) the Cantata was a step above the Calinda but not worth the double price differential to me. I would say that the 104/2 is more than a step above the Calinda. Of course that is comparing what I am hearing now compared to 39 years ago.
Both are excellent speakers and both would benefit from a more powerful amp than your current Sansui. Even if you went with the Cantata, an amp upgrade would be beneficial. The 104/2 can sound very good with low powered amps but really open up with more wattage and current.