crossfading

i'm trying to build a patch that would enable me
to beat juggle with a dvs and only one stereo input in conjunction with midi.
what i'm basically trying to do is route the signal from the tt through a
mixer then to ableton. i want my patch to take the volume of the signal
coming from the sound card and use it to control a gain control on another channel (so far i haven't succeeded in "getting" abletons cross fader).
i used plugin~ to snapshot but the numbers i'm getting are -70 up to about 6
which is normal but the problem is that when there's no volume it sends 0 instead of -70.
how do i go around this? should i use some sort of an amplitude object?