i need help with sound quality(i need full ,thick,sound)

ok im trying to decide what i need to buy to make my beats sound more thicker or fuller, i use nuendo 2 on my computer but the only thing i have hooked up is my mpc2000xl and my motif going into a dj mixer and my dj mixer going into my computer , nothing else , do i need a audio interface or something inbetween my dj mixer , or do i need to replace my dj mixer with something else?, cause im just tired of hearing other producers beats on myspace bumping out of computer speakers and then when i play my beats they sound kinda weak , is there any kind of audio interface i can use to make my beats fuller/thicker, i have a interface on layaway from tascam , and i also thougt about buying the firewire one that cost around $500 but i dont wanna spend any money on firewire for my computer i just want usb.

RME hammerfall is the best interface I know for a certain fatness in the beats. the old one works with a PCI Slot (it's ol' fashion, but it's still a killer), or there is also a RME firewire interface.

the other solution is a goog mixing desk. mackie is know for a fat sound.

and of course mix down your tracks really well. seperate the different freq.


cheers*

thats another thing i got a problem with , i dont know how to mixdown right , the only thing i mess with is the bass and treble when i do mixdown and when i do it in nuendo it sounds even worse especially when i add more bass to it to get it to sound full, starts to sound distorted