the mixer, will provide a stronger/possibly better sounding input, than the roland preamps will give you.
if you have the channels, and the inputs, depending on how many tracks you can do at once, i'd go into the mackie.... dry, into the vs.
then, mix the drums as you like, with eq and effects, down to a 2-track stereo sub mix.
there's nothing wrong with going through a mixer before it hits the vs, and depending on the quality of your mixer, you can boost the signal before it hits the preamps.... dropping the input value on the input knob to the minimum it needs to get full signal.... and getting a good signal without distortion, from your mackie, is the way to get the highest fidelity into the vs.
that way, the vs preamps and digital convertors aren't having to work so hard, and wont put as much of the 'roland' sound on your input signals.
the next step up from that, would be a digital mixer, and bypassing the vs preamps altogether.....
but you can only go into the vs digitally with 2 mono tracks, or one linked stereo pair.
does that make sense?
me, if i had the mackie, AND a digital convertor, i'd take the kick and snare, run that through a mixer or preamp, send those signals to a digital convertor, and go into the vs digital for those 2 tracks... then send the rest of the kit (overheads, toms, hi hats) to the mixer, and individually out to the rest of the available vs tracks.
if you're a good mixer, you could probably even get away with a stereo output from the mackie mixer (with everything on the kit minus the kick and snare), and the 2 inputs from the snare and kick coming in digital.
that way, you'd only have to use 4 tracks total for the whole kit.
but you'd be locked into your 'stereo' kit mix.......
it's all about being able to re-mix later.
what do you have total, 8 inputs?