Music Composers Unite!
I've had this problem too, that's actually how I fell on your post through Google, and I've found a solution that can sometimes fit.
The above screenshot is using Guitar Pro 5, so I imagine it's similar in GP6, but here's what you can do:
(from left to right): You've got the Track number, the name you give it, Solo, Mute, port number (mine above are all 1's), then you've got Channel 1 & 2 ( under Ch and Ch2 ). You can right click an existing on and "link" it to another one, this way you can free up some channels for tracks which you might want more control (such as volume and panning). Of course, it's not always the best solution, but in some cases, if you know 2 or 3 instruments can sit at the same panning spot (and volume), you might as well link them to free more space for the extra channels you'd want to pan around (or volume) independantly. Hope this helped.
I currently only have GP4 installed, but have GP5 & 6 on my other machine.
If I try this in GP4, the linking works but the linked channels share the same instrument.
Is that what you mean? Or do you mean that linking them shares panning and volume but the instrument is different?
That would basically solve most of that problem for me, so I hope it is in GP5 :-)
Thanks for replying!