Vinyl way too quiet through headphones

I have a Music Hall MMF-7 turntable (with high output MC cartridge), connected to the pre-section of a Plinius 8200 mkII integrated (with phono gain setting set to the low gain MM setting, since it's a high output MC I'm using). From there I go line out to a Perreaux SXH-1 headphone amp, and out to a pair of Etymotic ER4S's.

The volume is too low. I set the volume on the Perreaux almost to max, and only then does it become a reasonable volume. By this point, however, the amp really struggles (clicks, distorts), understandably because it's at max power.

Any ideas how to fix? CD's sound terrific, but the volume from the line out of the Plinius is too low for vinyl. I also have to turn up the volume pretty loud when listening to vinyl through my speakers, but the Plinius set to about 12o clock position works just fine. I have been told setting the Plinius to the high gain phono setting would be a bad idea, and amplify the volume of my high output cartridge way too much.