Based on what I heard at RMAF with the 50A driving the Wilson Benesch Curve loudspeakers (88dB, 6 ohm nominal, 4 ohm minimum), I would think using the 4 ohm outputs on the 50A would work with your 90dB, 4 ohm nominal loudspeakers.
However, I wouldn't buy the amp without being able to hear it with your speakers. It's too expensive a proposition to take a flyer, IMO.
However, I wouldn't buy the amp without being able to hear it with your speakers. It's too expensive a proposition to take a flyer, IMO.