dr. joe is essentially correct. One of the ways to see if the powersupply and the circuit design is able to deliver the juice, is the ability to run at double power in at lower impedance. I believe that many audiophiles greatly underestimate the peak power required on good recordings if you are listing at concert hall volumes. Many amps do not have the power supply capable of feeing the amplifier at peak output. I think many tube amps get a bum rap in the bass department because they are essentially underpowerd and don't match well to the speaker's bass impedance curves. I own Dunlavy SC-V's and on recent thread on the best amp discussed some of these issues in more depth. If your speakers have a sensitivity of 1 watt for 90 db in your room the peak power requirements for a row 10 experience of Mahler or Stravinsky would take about 250 watts with no headroom or loss of power due to impedance curve mismatch. Throw in an extra 6db of power to cover both and you are in the neighborhood of 1 kilowatt. High power amps or high efficiency speakers are required for a realistic reproduction of the technically suprior recordings.
High current or high wattage amps
I have somewhat difficult to drive speakers 86db 6ohm, the manufacturer of the speakers recommends about 200 watts to "open up" the speakers for the best performance. One amplifier manufacturer recommends higher current amps as being more important than the high wattage with the more difficult speakers. If my listening levels are not loud and the room is not large (16x30x7) is current a more important consideration?