I have SPL. I tried the Matrix option when I got the amp, but I didn't notice almost any change. It depends on recordings whether there is a benefit or not.
I have a few CDs that are completely useless for listening to headphones. I will mention a few authors, an album from Talking Heads, Jethro Tull, Rare Earth, and probably a few more. These are older recordings, wholly made for speakers.
When you listen to them, you have a heavy weight on one side of the head and nothing on the other.
I still didn't listen to these albums after I got SPL Phonitor XE to see if there was any difference and if they became listenable with the crossfeed option.
I don't have bad amps or DACs, and I wonder how an even more expensive amp or DAC would solve this kind of recording.
I love listening to headphones, and I love different experiences from speakers. If I get the same feeling, I wonder if I would be a headphones fan.
But the thing is that some recordings are not listenable at all with headphones, at least for me.
Cheers!