Not sure, exactly...
But you'll probably need a microphone preamp, or better yet, a mixer to boost your levels before they get to the VS 840. The digital mixer and preamps on the 840 suck, and if you check out the troubleshooting page in your manual, it probably says to get a mic pre if your levels are low.
To make your verse louder, why not try bouncing the track w/ effx and correct the low part using the faders. If you use the compressor/limiter type effx patch, that might help also.
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wawazzat?
Just try not to bounce more than once on each track