I use a pair of Threshold S500 II's to drive my Infinity RS9 Kappa's. These amps have been refurbed with the main power caps replaced, bias adjusted and various other updates.
I cannot imagine any amp better controlling the bottom end of these speakers. The K9's have an impedance dip at 30Hz to around 1 ohm and these amps have no issue with it just providing overwhelming power to the speakers.
At the other end of the spectrum these amps have remarkable fine detail and definition with pinpoint sonic placement and correct spectral expectation.
I would concur with your thoughts that the 500 will sound like a 300 as I have both. I also have an SA2 and a 400a as well as a Cas1. They all drive infinity speakers with tough impedance loads although not quite as severe as the K9's. Just great amps!
I cannot imagine any amp better controlling the bottom end of these speakers. The K9's have an impedance dip at 30Hz to around 1 ohm and these amps have no issue with it just providing overwhelming power to the speakers.
At the other end of the spectrum these amps have remarkable fine detail and definition with pinpoint sonic placement and correct spectral expectation.
I would concur with your thoughts that the 500 will sound like a 300 as I have both. I also have an SA2 and a 400a as well as a Cas1. They all drive infinity speakers with tough impedance loads although not quite as severe as the K9's. Just great amps!