I also use HifiBerry's AMP2 to drive a pair of old Kenwood speakers with a dedicated subwoofer (it's a 2.1 set out of the box), and boy, that thing's impressive for its size.

It has a Burr Brown DAC and a Class D 2x30W amplifier on board. It has delicious sound.

... with a decent <100$ DAC like Khadas tone board

You'll probably want an interface that has TRS/XLR outputs instead of RCA unless you want to get a weird cable. Focusrite Scarlett Solo would do the trick nicely!