enough watts to drive these speakers? Help?

Your calculations are a little optimistic based on my experience and will vary according to speaker design. Having said that, i don't see a problem with 8 - 10 watts of power feeding "normal" impedance speakers in this size room. That is, so long as one doesn't expect "thunder" and / or the amp uses tubes in the output stage. Tubes overload much more gracefully ( as a general rule ) than SS designs, producing more listenable results even when the amp is temporarily over-driven. Something along the lines of a 300B ( or something similar in output ) should work pretty well. Just be careful as some small amps are WAY over-rated AND don't like low impedances at all. Sean
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I use a 90db efficient speaker.I was happy with the InSound/Omega Mikro 10 w/ch prototype V amp,but settled on a set of Viva Verona XLs {26w/ch,pure class-A}.
Your first watt will produce an 89db SPL,at 10 watts you should yeild a 10 db increase in SPL.Doubling the power will add 3db.
I would be more concerned with the impedance presented by the speaker and complexity of the crossover.

Your calculations assumed that your friend would be listening at 1m (3.3ft) from the speaker in his bedroom. Would that really be the case?
If not, one loses 6dB when one moves back from 1m to 2m. Then one loses 3dB when one moves back from 2m to 3m. If your friend is 3m (~10ft) from speakers, the 89dB efficient speaker yields 80dB SPL at his listening position using 1W. To get 90dB SPL, he'll need 10X the power i.e. 10W. At this pt. the amp runs out of gas. There'll be a 3dB increase in SPL owing to 2 speakers i.e. stereo music. Room can re-inforce to some degree but it is hard to tell.
Ill designed xovers in the speakers can eat up some watts.
If he's willing to not crank it up, 8-10W/ch should be fine if everything else has a reasonable design (a bit nebulous but I hope that you can understand what I mean).

Bombaywalla, wouldn't moving back from 1 meter to 2 meters result in a 3 dB loss, not a 6 dB loss?