I ask because you need to be careful and check whether your amp has a common ground or not between left and right. If it doesn't have a common ground I don't think you can connect it like that. You might blow up the amp. I'm not an electrical engineer but I've asked this on the other threads and several people have told me this
I can't stress what you have stated. I believe a lot of amps don't have the common ground feature. While someone could have the desire to use a speaker amp to drive the headphones, there's also a likely chance that the amp could fail. Also, driving a pair of headphones with dynamic drivers is different than drive a pair of ortho headphones. The ortho headphones can take a lot more power. I know the Superlux can take only about 300 mW of power.