I have the same question.
One solution is to use "Multi Instruments" from the instruments tab, there you can add multiple instruments/vsts and decide how they get triggered.
But that's no real solution. For example I have two *existing* instrument tracks and want to move them into a multi instrument. That is not possible. Also instruments/vsts have no high-dpi support compared to their normal version.
Also there is no other instrument that can be routed to trigger different tracks. The Impact XT can only play samples, but it would be useful, if it could trigger tracks, so I can build drum sounds using mai tais and trigger the different parts of the drum by the impact xt.