Ichigo, of course it's not possible to make a precise analysis at long range, but some comments are appropriate. First, the amplification process has no ability to affect "soundstage" as long as the channels are separated by an amount which any modern amplifier far exceeds. Secondly, if the amplifier has flat response down to 20Hz, which any receiver of the quality which we'd seriously consider does easily, it reproduces bass well. Bass is no different in this respect from any other frequency range: at a given sound level 40Hz requires the same amount of power as does 400Hz or 4000Hz. If the sound level isn't precisely identical when comparing two units however(proper blind tests require matching to within 0.1dB), then items such as sound-stage and bass will sound different, not because of some mysterious quality superiority, but simply because one is being played a little louder. Casual listening not under controlled blind conditions can easily mislead us and can't be relied upon to make judgments. Louder usually sounds better.
Since it summarizes the point well, I'll again cite the editor of the Audio Critic in
"Electronic Signal Paths Do Not Have a Personality!" for a brief explanation.
