Pass & Aragon with Focal speakers

I have this ever evolving multi channel audio system. Current setup consists of Focal Electra 1037BE, Pass X3, Aragon 8002, and Linn Unidisk SC. X3 is basically three channel version of X-150, rated for 150wpc at 8 ohm. 8002 is a low power version of 8008ST with rated power at 125wpc at 8 ohm. X3 powers the main and center, and 8002 powers the rears. Unidisk SC has variable level output, and it's driving the power amps directly.

Focal Electra 1037BE is the newest addition to the system, and it replaced B&W Nautilus 804. 1037BE sounded really good, but sounded somewhat lean compared to what I have heard elsewhere. The impedance curve of 1037BE is rather interesting. It's 4 to 6 ohms below 1KHz, and 10 ohms and up above 1KHz. Not the worst there can be, but still a demanding load.

Today I decided to experiment a little bit, and swapped X3 with 8002. Much to my surprise, 1037BE powered by Aragon 8002 sounded much fuller in the bass. Pass sounds tad more musical. Aragon sounds a little sterile, but much more tonally balanced.

It basically reaffirms the importance of proper equipment matching. But I'm still baffled by the result. X3 is from the older design, but X-150, which it is based of, is still a well respected amp. AFAIK both amps should double down the power into 4 ohms.

Could it be mismatched impedance? I think the input impedance for Pass is around 20KOhm. Is it not high enough for Unidisk to drive it directly?