Matrix amps generally work fine without needing a power conditioner. 

Some poor power conditioners have even been known to make things worse, when they are not able to keep up with the changing load on them.

Generally, you only need a power conditioner if the mains is very poor and varies in voltage a lot.  Use a good quality conditioner that can maintain the output within 10% of the nominal supply voltage.

If you suspect that your mains supply may include significant voltage spikes, a conditioner that can limit the incoming voltage (often called a surge arrestor) can be useful.