The main difference between the X1 and X2 is that the X1 has built-in bass equalization applied to give the Evolution subs a flat response. Without the EQ, the Evolution subs would naturally roll off at 58Hz (-3dB). You can find this in the Stereophile review of the NHT Evolution T6 system. Also after looking at the block diagram available at NHT's website, their subsonic filters vary (X1 is 26Hz vs X2 at 15Hz) and their lowpass frequency ranges differ (X1 is 50-140Hz while the X2 is 30-220Hz). The X1 should only be used with NHT Evolution subs (unless you want boosted low bass). The X2 is for everything else.
NHT X1 and X2
I have the U2 sub with along with seven M5s for the HT set up. The X1 cross-over supported by 2 of the A1 mono-amps. NHT manual states that the X1 to be used with the Evolution lines while the X2 for non-Evolution lines. I have check both the X1 and X2 spec, they are identical except for the X2 logo on the unit. All the features and spec are the same on the X1 and X2. Can somebody tell me what if I use the X1 to set up with the Classic line?