Should I buy a DAC?

I have the money to spare And i wanted to get an Objetive 2 amp/DAC from mayflower, i have 35 ohm Sennheiser HD 380 pros with 52mm drivers.

first off, would this make a difference in my sound quality?

second, since it will be running off the audio from my pc what is the point of converting it into an analogue signals if its already coming out the back of the pc that way?

clearify if i dont know what the hell im talking about (which in this case is most of what I just typed).

*edit* I just looked at the pictures, does it go through the USB or the 3.5 mm connector?

You don't need the amp at all for those cans, pick up the DAC and that's really all you'll need, unless you plan on picking something up like one of the 250Ohm+ Headphones from BeyerDynamic, or other high impedance headphones.

The DAC/Amp can be used either with 3.5mm in or USB in. It is preferred with the USB in to eliminate the issues with the on-board solution, interference and the higher output impedance which is why you would want the DAC to improve the clarity and fullness in the audio you hear. 

A DAC alone doesn't have the amplification needed to drive headphones, you must be thinking about a DAC/AMP combo.   Single DACs do not have headphone jacks.

DAC's signal is very weak to drive anything, because is designed to be coupled with an AMP.

I'd probably get some better headphones then you can invest into a better setup.

thanks for all the input and clearification.