21 watts will lead to unhappiness. If you want to listen to very quiet music, don't waste the money on the 1.7's either. I've tried maggies with 12, 17, 20 & 40 watt amps and was always left wanting more. No bass for starters and they break up way too easily.
I like Maggies but not without about 200wpc or more...
I like Maggies but not without about 200wpc or more...