How to connect HY-M285 Solid State Relay?
Using the voltage rating marked on the part for dc, apply this to V+ and V-.  The tolerance of that voltage “may be 15%”  like 5V on a 6V part, (edit: OMRON says 5V +/-1 = 20% ok) but 6V might be more reliable when hot or might not make any difference. But 12V on a 6V part will damage it. The trigger current is small like &lt; 15 mA.
Using an only collector NPN switch to trigger and V- or test with dry contact switch or wire shorting Trigger to V-, will activate the Triac.
PNP trigger means negative voltage trigger relative to V+ or in this case 0V= V-.

since it says near 0V for activating, I can assume the current limiting IR resistor is included  to drive the isolated Triac output.
Since it is encapsulated, no heatsink and low power dissipation e.g. a couple watts max loss at a low current rating of 2A.

But the woofer amp will have large energy storage caps to supply power measured in mJ or J.  Thus your surge current could be 10A your rated current for the 1st cycle. They might be able to handle this. But check the temperature rise when doing this. If it is a zero-crossing type switch, the surge is reduced greatly by the rise time during switching.  If not it is possible to synchronize your power on pulse with line frequency somehow if it does appear too hot when turning on, since it is only rated by heat rise for 2A into a non capacitive load.  They have carefully removed the OMRON logo so you buy their part instead, so good luck ;)