Sonic Defender
Headphoneus Supremus
Hi-fi man makes a speaker amp accessory that allows you to connect the headphones directly to any speaker amp by using just regular RCA cables connecting from the box to the speaker. Have you seen this?The box has a built-in attenuator so as to protect your cans from exploding
It is still a series of resistors. Not needed with a solid state amplifier, in fact, it would degrade the sound quality. Now with tube amplifiers this type of device is needed, but not with solid state gear. Go straight from the speaker terminals for best results.