comparinf Octave RE320 to Threshold S500 II

I have a S500 II, 250 watts but manual does not state ohms amplifier, that I would like to power up and compare  to my present Octave RE320 kt150 150 watts peak into 4 ohms amplifier. Speakers are KEF Blades. Preamp is Octave HP700SE. Source is Naim NDX2. All have extra external power supply additions.

Any thoughts/help would be appreciated!