Which chip/board to drive a Subwoofer?

[doctormord]

The cheap boards usually have more problems with higher frequncies, because of insufficient output filters.
If anything is important about the output filters in this application, you should check the temperature of the inductors.

Energy is "moved" in the LF, not the HF, so heating and Ldrop vs. Ispk is more a concern at low frequencies but your ears are that sensitive at low frequencies to THD/distortion. (Beside this, speaker distortion rises with lower frequencies)

 

[Kjeldsen]

Maybe this - note that it is digital input only
Hifimediy DDX320v2.3 - 2.1 Digital Amplifier

 

[Kjeldsen]

also this one, but freight makes it almost to 200$

2 way full range Speaker Amplifier Board RMS 600W Class D Amplifier Plate Built in DSP module with Aluminum Radiator-in Professional Audio, Video & Lighting from Electrical Equipment & Supplies on Aliexpress.com | Alibaba Group

 

[Jerms]

MiniDSP plus MiniDIGI 2x4 plus a bundle of TPA3116s is probably about on the money.

https://www.minidsp.com/products/minidspkits/2-x-in-4-x-out

J.