How to control mic and mix volume while recording

[Drew Stephenson]

I'll re-rig without the Mackie for awhile and see how it goes - especially beneficial if I can solve the headphone mix issues with the software.

I'm not sure that's going to work. You can set up different mixes in the mix-control software but if there's only one headphone output then you're still back to square one.

[resistorman]

The interface has 4 line outs, and I assume they're individually addressable from software. Seems to me you can send a couple with an alternative mix to the Mackie and use its headphone out.

[Sam Spoons]

Still not sure why you need the Mackie? I'd ditch it and use the inputs on the F'rite for mic(s) and other instruments then send a stereo pair from the F'rite to the headphone amp. That way you can have separate mixes going to the HP amp and the F'rite HP output. The mixes can be achieved from your DAW or, I think, using the F'rite mix control app.

The Berry HP amp fed from the spare line outs from the Scarlett will provide the second mix.

[Drew Stephenson]

Still not sure why you need the Mackie? I'd ditch it and use the inputs on the F'rite for mic(s) and other instruments then send a stereo pair from the F'rite to the headphone amp. That way you can have separate mixes going to the HP amp and the F'rite HP output. The mixes can be achieved from your DAW or, I think, using the F'rite mix control app.

The Berry HP amp fed from the spare line outs from the Scarlett will provide the second mix.

You will need to make up a 2xMono-balanced to 1xStereo-unbalanced cable though!
Easier to just plug into the Mackie as Resistorman suggests.
Which does bring us back to my second suggestion...

[Sam Spoons]

True enough but the OP said the Mackie HP output was cutting out so it seems sensible to bin it rather than the, apparently working correctly, Berry HP amp.