The biggest factor is going to be the sensitivity of the speaker. Then their impedance. And then the listening distance.
Small speakers, like the Studio 20’s tend to be less efficient.
You’ve got 10W at 8Ω (or 20W @ 4Ω, 40W @ 2Ω ) to play with from the HSA-1b.
Running flat out, and at max-volume, the HSA-1b would drive the Studio 20’s to a PEAK volume of 98 dB/SPL at 6 feet away. That’d be an average level of 80-85 dB/SPL (depending on what sort of music you listen to). At 10 feet away, that’d drop to 93 dB/SPL PEAK.
Flat-out is really not how you want to run an amplifier. For one thing it’ll be at the peak of its distortion profile. For another you have no headroom. It will work, and its safe, but it’s going to be a long way from getting the best out of the amplifier and the speakers both.
You really want to be looking for something around 93-95 dB/SPL (at 1W @ 1M). That’d get you to 100-103 dB/SPL PEAK, but would give you some headroom at an 80-85 dB/SPL listening level.
And then once you’ve got the sensitivity at a better level, a lower impedance speaker will help you get the most power on top of that, further expanding the headroom and putting the amplifier closer to its sweet spot.