I'm not familiar with the SA-2 amps (I KNOW of them, but have not heard them or used them at all)...
I CAN say this, though...I've owned the 2.5i's in the past (and for quite a while). The benefit quite a bit from bypassing the internal crossover (biwiring). I would imagine bi-amping would be even better, but i've never set up a system in this configuration, so i do not know the intricacies/ details of how to properly set it up.
But at the very LEAST, biwire those speakers... You'll get a much better level of clarity in the midrange, not to mention better bass definition/ less muddling of the sound.