Sam1e@ I noticed the recommended operating impedance range of your Fosgate Signature headphone amp is from 50-500 ohm but your LCD-3's impedance is only 45 ohm . I have the feeling that your LCD-3 may not work at its best with Fosgate. Incorrect impedance will affect the overall frequency response and cause some distortion. However HD800 has an impedance of 300 ohm which should work better. May be I am wrong.
LCD-X has an impedance of 22 ohm which is even lower than LCD-3 but my HPA-200SE can cope with headphone impedance from 12-600 ohms while Yulong A18 can work with 16-600 ohms.
No problem according to Jim Fosgate when I checked to see if the Fosgate would cope with my 600ohm Beyer T1's, it's quite possible that the LCD-3's will sound better with a different amp, but there's no apparent problems that I can hear with the Fosgate/3 combination and no shortage of volume.