Help! Source Output Too High for Headphones

I'm looking for any suggestions on how to reduce the output from my source, a Sony XA5400ES CD player. 

I run the CD player to my headphone amp, either a iFi Pro ican, or a Woo WA22 amp. With any of my headphones 

which are high or low efficiency, high or low impedance, I can only turn the volume up 1 or 2 notches, or below 9 o'clock.

There is no volume adjustment on the Sony, unlike my Oppo 105D. 

Can I put anything in-line to reduce the output?

Thanks!