The Bryston amp is a full range regular power amp. This is more than you need for a subwoofer.
For a subwoofer power amp high frequency response is unnecessary. Only slowly changing voltage will be amplified.
For a subwoofer power amp, a very low level of distortion is unnecessary. Subwoofer drivers generate lots of harmonic distortion (so that a little added by the amp is not important) and this distortion is not objectionable in the way that it is at mid and high frequency.
Therefore, an amp that is not intended for any use other than a subwoofer can be built for relatively low cost. I have used several from Parts Express, and they performed well. There were no Hum problems.
For a subwoofer power amp high frequency response is unnecessary. Only slowly changing voltage will be amplified.
For a subwoofer power amp, a very low level of distortion is unnecessary. Subwoofer drivers generate lots of harmonic distortion (so that a little added by the amp is not important) and this distortion is not objectionable in the way that it is at mid and high frequency.
Therefore, an amp that is not intended for any use other than a subwoofer can be built for relatively low cost. I have used several from Parts Express, and they performed well. There were no Hum problems.