I have heard the Di Capo i's on a Cary 300B , it was not enough power .
While these speakers are rated at 92db. the resistance is down to 6 ohms nominal . I have these with a 35w P/P and it is quite nice .
I A/B'd the Sli-80 with a Cayin A88-T on the Di Capo i's and could not hear that much of a difference , certainly not enough to justify the higher price of the Cary . I bought the Cayin and was quite happy until it came time to bias it . What a bear ! I passed it on to the next owner !
I am now using a Primaluna Prologue 2 . I like it much better and it is even less money . It has better top end extention and more clearity , those things that you don't know your missing until you hear them . With stock tubes it is not as warm as I like . After I rolled the input tubes it came much closer to that traditional tube sound characterized by the Cary and Cayin . Now that I have rolled in some EL-34's , I am quite happy . It is , to me , everything that the Sli-80 is and more .
On a side note...if I were looking for a Cary 300B SE I would look at the LX20 version of the sei . It puts out 20 watts as compared to the sei's 11 watts . But they are tough to find .
Good luck .