Raiden Fader RXI-F2 used in FX loop

New to the portable realm, but eager to learn. I have a technical question regarding the use of the Raiden Fader RXI-F2 in an fx loop on my Rane MP2015. The purpose is to have cutting/scratching capabilities on this mixer. I run the fx loop to the sub channel and any channel that goes to the sub channel is effected. In essence, I can scratch that channel. The issue is the audio signal drops drastically when ran through the fader. I heard that a headphone amp will boost the signal back up after the fader, but don't want to prematurely purchase something that doesn't work well.

Any experience with a similar situation and possible remedies are welcomed. Or, even a technical explanation why it's happening so I can research the best remedy myself is great as well.

Thank you in advance for any advice.