I do not want to blow up my speakers, but i also know that Insufficient power can also be harmful.
Have no fear, the volume knob is there! When comparing 10 W amp to a 100 W amp, that is the maximum power that the amplifier can provide. It does not mean that the latter is 10 times louder (gain) than the former. It's also up to how much the speaker "draws" power (impedance), so high impedance speakers will not draw the max power even if you turn it to maximum volume. "Insufficient power" is relative to what you use for. You cannot scorch a 200 W speaker with 20 W amp. Speakers usually have a sensitivity of 84-92 dB / Watt at 1 meter distance, so you usually don't need many Watts anyway. Except for bass-heavy content, but it's not the bass driver that get's fried first. And if you use a separate powered subwoofer, that problem is solved.
The best way to add a powered sub to a stereo system is through a DSP processor. There are many kinds, but which one is right one for you is up to what you expect it to do. Personally I'm a fan of miniDSP products and as such my first option would be something like
miniDSP Flex, but that's only the preamp so you need a power amp too. MiniDSP products are very powerful and versatile, so despite their price, I consider them to be good value. One attractively priced competitor would be
Arylic , I'd suggest a model that has DSP and output for active subwoofer. I cannot point to any of their products, because I cannot comprehend their catalogue, there is no clear indication whether a product has a DSP or not. There are some problems with Arylic, like their products are not very powerful, their favorite chip amp is rated for a little over 30 Watts clean power into 8 Ohms (
https://www.ti.com/document-viewer/tpa3116d2/datasheet), so if that runs out, you need something else. You also need to pay additional fee for the software and if you get a new computer, you need to buy the software again. But it's still considerably cheaper than miniDSP.
