Hi Jeff,
I largely agree with Malcolm, but would qualify it as follows.
If you have a room around 15' x 25', and listen to orchestral music at around 105dBA at ten feet, then with 92dB/watt/meter speaks there will be moments with the 55W AKSA when you will discern slight strain. If you do the sums (hope I get it right) for a 92dB speaker, at two meters, it will be 86dBA, and at three, 83dBA. So, at one watt, you'd lose 9dB to 83dBA from a point around 10 feet from the speakers, but there are two of them so add approx 2dB (not a scalar addition since the channel information is not the same) to 85dB. We want 105dBA at the listening position, which is 20dB more and comes to 125dBA at a point 1 meter from the speaker, and this is around 2exp3 times the power requirement, plus add a little more for the extra 2dB, say 9 times, viz 9 watts. In practice, however, you might have to push out peaks around 8 times more than this (24dB higher), at 70 watts or more.
However, that's LOUD, and most people, unless they are deaf, will listen at lower levels where you will never notice any problem. But the 100W AKSA will give you another 3dB of reserve, which is immediately noticeable, for want of a better word, as 'authority'. There is no doubt the 100W AKSA has extraordinary grip at low frequencies, and this does enhance realism for large sounds like orchestras, particularly at higher volume.
I recall AES figures some years ago for 90dBA/watt/meter in smallish rooms which argue cogently for a minimum 1200 watt amplifier. This may be credible from the numerical, physics standpoint, but in all honesty every 1200 watt amp I've heard sounds terrible, and negates all our efforts to achieve a clean and musical sound. Clearly there are many who are very happy with their 100dB/watt/meter speaks and an 8W 300B SET amplifier, and so I'd suggest that a 55W amplifier will certainly fit the bill for moderately efficient speakers in a not-too-large room. But if you love strong bass, and rock 'n roll, then maybe you should consider the 100W AKSA!
On balance, it really comes back to your budget. The 55W will be fine, but you'll need to turn the wick down about 3dB vis a vis the 100W AKSA; scarcely discernible, but to an audiophile, a subtlety you'd certainly notice after a time.
Cheers,
Hugh
