outboard pre into Mbox; setting "unity gain"?

[tokyofan]

I just starting running a Grace 101 into the 1/4" input of my Mbox (bypassing the microphone preamp circuit) and am wondering if there's anything I need to calibrate on the Mbox. The guy at Sweetwater said to "set the Mbox to line" (OK) "and the gain knob at unity gain if possible. This way the audio signal is not being modified by the Mbox." OK, how exactly do I achieve "unity gain" and is it really necessary? A little confused on this.

[tele_player]

Well, since the issues for gain staging are sound quality and headroom, you could just set it for wherever sounds best. I'd use the 'line' setting, with the gain all the way down.

[albee1952]

Ditto. Likely the Grace is designed to output a +4 signal and the Mbox line in is designed to recieve a +4 with the gain all the way down.