Midi Playback Problems, complex PC MIDI won't play on MAC Options

Hello and I hope I'm in the right forum for this one.
I've got a lot of semi-pro MIDI produced on PCs using Turtle Beach sound cards and QSE, Cakewalk and other sequencers. The more complex ones (with a lot of events and controls) always bog down and stop when I play them back on my eMac G4, 1 gig memory using the internal QuickTime synthesizer. Doesn't matter which software program I use to play the MIDI, I suppose it all uses the internal synth. What is the solution here? I want to be able to play and edit these MIDIs on the Mac. Thanks and regards!

Thanks, lepetitemartien, for your reply.
The issue, in the nutshell of your choice, is that the more complex a MIDI file is (more events such as notes, controllers, etc.) the less likely that it will playback without stopping on an average quality MIDi playback device. The QT synth, many on-mainboard sound chips on PCs and numerous PC soft synths simply will overload and stop when encountering too many MIDi instructions. A high quality soundcard, such the Turtle Beach Santa Cruz in my PC, can handle 16 tracks filled with notes, controllers and other events, with a faithful playback without a pause. Processor power could be a problem, not on the AMD PC, but I don't suspect that my 1.25 GHz PowerPC G4 with 1GB DDR SDRAM would have any problem. If you can direct me to more tech specs on the Mac family - such as is there an onboard sound chip that handles the MIDI playback instead of a soft synth - I might be able to learn more about what I don't know about Macs. Thanks again.