The price of those speakers seems to be in line with what they are sold for on the used market from what I can see:
Used B&W CM5 S2 Loudspeakers for sale on 400+ second hand hifi sites & shops. Use Hifi Shark to monitor pricing and global availability
www.hifishark.com
We assume that the technical data is correct, the speakers have 88 dB sensitivity and let's say they are 4 Ohm speakers.
We assume that they do not constitute a particularly tough load on an amp so any amp that can handle 4 Ohm speakers (basically all amps) is ok.
For normal listening volume in a normal room around 30-50 watts in power would have worked for me. But I don't know if you like to play at really high volume with very dynamic music, if so choose an amp with as much power as they can handle. 300 watts according to the spec. I doubt that they can be fed with that power continuously, small dynamic eruptions maybe but they are temporary.
Even IF they could do it, it would sound awful if they were pushed at 300 watts continuously. High distortion plus hearing damage (eventually) on top of that.
(they are home hifi speakers not PA speakers)
B&W CM5 S2:
Edit:
The amplifiers you are considering are popular here at ASR. If I remember correctly regarding the Douk Audio A5, choose the 32 V/5 A power supply, which results in 59 watts into 4 Ohms. With a more powerful power supply that amplifier seems to get quite warm. You can read about it here:
This is a review and detailed measurements of the Douk Audio A5 stereo class D amplifier. It was sent to me by the company and costs US $99.99 as of this writing on Amazon including free shipping. I really like the look of the unit. The control on the right turns the amp on and adjusts the...
www.audiosciencereview.com
An advantage of the Douk Audio A5, according to Amir in the test above is:
The knob on the left adjusts a high-pass filter which is nice to have to tailor the bass response for typical bookshelf speakers this amp will be driving. And allowing subwoofer integration..
