You may be referring to the S&V test of the A3000(140 watt rating)rather than the A1000(105 watt rating), but in any case, there's so little difference between the maximum power outputs(a dB or less)that they can be considered to be essentially equal in that regard. I might point out that "all channels driven" at full power isn't a realistic scenario in home use outside a testing lab, and little attention should be given to a lower number for that measurement.
Either the 991 or the 8063 should have ample power for playing your M60s at all safe sound levels, so choose on the basis of features and price. In both respects the 991 would appear to be the better buy. Among other features, it includes Audyssey MultEQ XT, which Dan Cumin praised in his S&V review of the 991 for the improvements it made to sound quality in his setup.
