Question for the Hi-Fi experts ??

First of all, just because you like the way your headphones sound doesn't mean they are more or less accurate than your speakers, but of course, it is all about the sound that you like. Most people are going to tell you that the answer lies in the interaction between your speakers and the room that they are playing in. The manufacturer of your headphones was able to balance the response because they knew the exact environment they would be played in.
I also think that it is interesting that you feel you can solve your problem with an amplifier. You should list your present system and room dimensions.

First, headphones ARE NOT speakers. They have no room problems at all [reflections,uneven responses] and they have to move only the small amount of air in your ears instead the whole room so it is much easier to get low bass. NO speaker is ever going to sound like a pair of headphones; they provide two completely different listening experiences. If you like the headphones that much better I would stick with them; you could spend a very large amount of money trying to duplicate the sound with speakers and I don't think you would succeed. If you want speakers judge then against other speakers, not against headphones. They provide a very different perspective on the sound unless you have invested in one of the devices which simulated the kind of sound we hear with speakers instead of having the sound appear to originate in the center of your head.

Stanwal,
That`s a very good answer. It`s like some wanting their car to handle and perform like a motorcycle.