Tascam Series 8P Dyna Analog Outputs To Headphone Amp

[John9999]

I have this connected to a Focusrite Scarlett 3rd Gen via optical adat, and I tried connecting outputs 1 & 2 on the 8p to a little Mackie headphone amp using a y-cable...two TS to a stereo 1/4". In Focusrite Control, I sent the main mix to those outputs 1 & 2. But no sound is coming out of the Mackie headphone amp.

What am I doing wrong?

Thanks.