@howardlee I'd say use the Pass labs as Preamp and get two of this Monoblock that is stable down to 2 Ohm. With incredible current drive and stable at all loads so are not load dependent.
Have tons of voltage swing to make sure the speaker movement of cone is aligned.
Get two of this - https://www.buckeyeamp.com/shop/amplifiers/hypex/ncx500/monoblock
Power delivery: 700 watts @ 2 ohm, 700 watts @ 4 ohm, 380 watts @ 8 ohm
You have so much headroom with this that you'd never lack for power delivery.
You'd connect them through the XLR Preamp Outs on the INT-60 and carry that signal via XLR interconnects to each monoblock XLR input.
Get two of this cable. Robust, does the job and doesn't get in the way of the signal - https://www.amazon.com/Units-Balanced-Microphone-Amphenol-Connectors/dp/B074XSDCG6