Isn't it 400w into 4 ohms? How could power be lacking?
Arh, just because a power amp has high wattage does not mean that power could not be lacking.
Power = voltage * current.
This amp could have a high (secondary) voltage transformer (that produces the 400W into 4 Ohms) but this transformer could have a very low current rating.
This would mean that this power amp would be (severely)lacking the ability to drive current into the speaker load making it inappropriate for use with current hungry speakers.
I believe (& correct me if I'm wrong) that Maggies, in general, are current hungry speakers. if the power amp cannot deliver current into such a load, the sonics are going to be anemic.
Hope that this makes sense....