Hi dexterflex,
I would definitely think about using the matrix with Vienna Instruments, that would most probably cut down your MIDI tracks to less than 50 MIDI channels. I know that this means to change your work-mode, but you will be A LOT faster plus get a better overview.
Especially with Cubase 5 and VST Expression this is very convenient to use. Here is a video tutorial on how to incorporate VST Expression.
On the other hand, you should get quite far with your i7 PC concerning VI instances. I have not tested out the limits yet on my i7 950 machine, but I think 160 MIDI channels might work. More VI instances will of course tax the CPU more.
Did you check out Vienna Ensemble PRO already? ThereĀ“s a free demo license available here.
Also, check out our videos on Vienna Ensemble PRO to get an overview.
Best,
Paul