I'm wondering if there's a way to use send effects in Qtractor, or if it's something that could be implemented. Send effects let you share a single effect (reverb is the classic example) among multiple tracks; it's very handy for ensuring a consistent sound across the mix and for reducing CPU usage (by replacing the separate plugins on each track with one, shared effect), and it's critical for using external effects, like Jconvolver, where running separate insert effects on each track is impractical.
Hopefully this will illustrate the scenario:
* a bus is created, and a 100% reverb effect is added to it (could be a plugin, or an insert to Jconvoler or some other external reverb)
* a "send" is created on each track, which routes a copy of the track's audio to the bus, without interrupting the signal flow on the track
* each of these sends has a gain control to adjust how loud the copy sent to the bus is; this allows the effective level of the effect to be controlled per-track
If that's still not clear, I described how to set this up in Ardour in more detail in this (rather lengthy) blog post.