Modwright KWA 150 and Proac D38R

Since you've already purchased the amp, then once you've hooked it up and played it, please report back. Your experience will be valuable to future readers.

BTW, the 250 watt specification relates to the maximum recommended continuous power the speakers are designed to handle. The spec has nothing to do with how well the speakers are driven by a given amp, but rather it informs you to be careful when using an amp with more power than 250 watts. Turning up the volume to a point at which the speakers require more than 250 watts may damage the drivers. The decibel level where this would happen on the D38R would be between 112dB and 115dB measured at a distance of 1 meter from the speakers (considering the 91dB/1w/1m spec). It's unlikely you would listen this loudly for long periods, unless you have a very large room to fill, but caution is still advised.

91dB/1w/1m:

91dB = 1 watt
94dB = 2 watts
97dB = 4 watts
100dB = 8 watts
103dB = 16 watts
107dB = 32 watts
110dB = 64 watts
113dB = 128 watts
115dB = 256 watts

I once owned Von Schweikert VR4 Gen III HSE speakers with Hovland capacitors. Those speakers were rated to 1000 watts per channel. Talk about being able to handle lots of power without blowing up!

107dB = 32 watts
110dB = 64 watts
113dB = 128 watts
115dB = 256 watts

Made a math error at 107dB. It should read:

106dB = 32 watts
109dB = 64 watts
112dB = 128 watts
115dB = 256 watts

The OP isn't asking about a match with 97dB/12 ohm Zu speakers.

He's asking about a match with 91dB/4 ohm Proac speakers.

Equating an amp/speaker match on 97dB/12 ohm speakers to an amp/speaker match on 91dB/4 ohm speakers demonstrates a basic lack of understanding of the topic.