I have always used Finale software and an Ensoniq SQ-80 synthesizer to compose / playback my arrangements for marching band (woodwinds, brass, percussion). I recently purchased a PowerMac G4 running system 10.2, and I would like to also purchase a new synthesizer or sound module to replace the SQ-80. Which unit is capable of accurately re-creating the sounds of all of these acoustic instruments?

I really haven't seen one piece of hardware that accurately does all acoustic intruments really well. It seems one does strings good and another does e-pianos goods etc. You might want to pick up some magazines like Keyboard and start reading some reviews to find the one that will have sounds to best suit your needs.

Another idea is to just buy a software sampler and then start a collection of acoustic instrument samples. I have ESX24 sampler for Logic and have some fantastic acoustic instruments for it. I have a grand piano sample that was about 100mb of samples combined and it sounds amazing. I also have a flute that sounds like a flute player sitting next to you rather than emulation. Sonomic.com and Primesounds.com are great resources for ESX24 sampled instrument sounds too.