SP2500 with Arcam rPAC external DAC

I'm running a PC desktop system with an SP2500 setup and a SoundBlaster X-Fi Xtreme soundcard.

I was given an Arcam rPAC external DAC as a present, but can't see how to connect it into the system, short of buying a new separate amplifier.

Am I missing a trick?

Does it make sense to try to connect the Arcam, given that the Soundblaster presumably has a built in DAC?

If I can connect the Arcam, would the sound quality be significantly better? I do have a fair amount of HD music.

I tried Corsair support direct.....they were very off-hand saying, basically, I didn't need an external DAC...the SP2500 system was good enough.