The human ear has been shown to be more sensitive to midrange frequencies at lower sound pressure levels (spl). Adding a subwoofer and a tweeter that you can adjust the volume separately from the rest of the system helps. Listening at lower spl limits the possible dynamic range but extends the lifetime of your sense of hearing. Hopefully your listening room has low background noise levels and/or is well insulated that would allow you to hear more without long term hearing loss.
Just what levels do you normally listen at? Until you measure you'll be speaking in generalities. Recommend picking up a spl application for your cell phone. Lately I've been enjoying big band streaming radio at average 60-70 dB but typically I listen to small ensemble jazz and classical at average 70-80 dB in my dedicated, well insulated 8ft x 13ft x 21ft basement room that's out in the country. Keep in mind that peak live performance spls in jazz or classical are 105 dB (but are very short) and rock live peaks are 110 dB (at longer exposures).
Highly efficient loudspeakers allow for more dynamic range, but the average spl needs to be higher to hear the low volume signals. Buy loudspeakers first, to match your taste and room, then find an amp that matches the loudspeaker manufacturer's recommendations. Look for sufficient power to provide a commanding grip for better resolution. The numbers are fascinating but only tell part of the story. Low efficiency loudspeakers, say 83 dB/w/m, would need roughly 500 watts to reach live rock levels while high efficiency loudspeakers, say 100 dB/w/m, would need about 10 watts to reach those same levels. But true, real world, specifications are hard to find.
