The experience that sticks out in my mind was when I brought my 100wpc Rogue Stereo 90 Super Magnum amp (KT120 tubes) to a friend's house to power his Maggie 1.7s. It seemed OK initially but after comparing against a more powerful amp, the sound was a little compressed and veiled on the Rogue. This same Rogue amp drove my Thiel CS2.4 with no issues at all but didn't have enough oomph for even the smaller Maggie 1.7 speakers.
My friend put his 400wpc monoblocks back on the Maggies and they came to life with effortless dynamics and transparency that clearly showed that 100wpc from the Rogue was not enough.
Also, if a speaker manufacturer says the recommended power is 25-150W, I would lean more toward the middle of that range (or more) for best results. That's just based on personal experience with the speakers that I have owned.
For example, Tannoy recommends 30-175W for my Tannoy Definition D500s (91dB 6 Ohm nom.) but with most amps they need about 75W or more to really 'come alive'. The one exception was with my 50wpc Krell KSA-50S, but I think (like BMW) Krell was ultra-conservative on their power rating.
And BTW, this is regardless of listening room size or volume level. An under powered amp is going to sound under powered even at lower volume levels in a smaller room. It's still going to sound a bit compressed. I had a similar experience with the Pass Aleph 3 and Aleph 30 (30wpc Class A) amps in another system. Some folks will say "so long as you listen at modest levels you'll be fine". That has not been my experience.
You'll have to judge for yourself. Try your speakers with that modest 20wpc, then try with a quality higher power amp. Enjoy!
