Amplifiers do not improve the sound quality of your music. What they do is amplify the signal (ie make the headphones louder). This might make your headphones sound better if they require more power to function optimally.
And android phones currently do not have a line out to connect to an amp. This will improve the line out signal and make the music sound more clear if your headphone jack is crap. So all you will achieve by adding an amp to your setup via the 3.5mm jack is increasing the power output.
What improves the music from your phone is a DAC (Digital to Analogue Converter) chip, or as you put it, the sound chip. The problem is that the current android OS's available do not support external USB DACs. Even iphones require a proprietary chip from apple to bypass the iphone's own DAC.
However, with the coming of the ice cream sandwich OS, google is rumoured to open up the USB capabilities which should allow for DAC and amp makers to utilise the mini usb port on android phones as possibly line outs or program the signal to go through it, allowing for external Dac support.
In short, no you cant use amps or external DACs with current android phones.