Well, the W5 is rated 40/80 watts RMS/Max. At PE, the MONO amps don’t have quite enough oomph, and I’m not talking about the ICE amps. Looking at 2.1 amps, the lowest I’d go would be one of the 15/15/30 watt units, just using the x.1 output. AFAIK, the other outputs should remain ok if unconnected as they are solid state, which usually has no problem being left alone. Now, you could go with one of the 50/50/100 units, just turn it down, and / or go with a lesser power supply.
To me, the most important thing, after the power ratings, would be the controls available on the amp itself. If it has a separate bass level and main volume control, then that would be icing on the cake.
Of course, your preferences may vary. 😄