Gostan,
Since you mentioned that you have 2-sets of speaker cables, and not the typical Y-setup (1 pair of spades at the amp side, 2 pairs at the speaker side), we suggest you try with singl pair of speakers, and it could be an improvement.
NuForce takes feedback at the speaker terminal, should minimize the benefit of biwiring. I would think that having a solid single wire is better than the extra soldered 2nd wire.