Crackling is usually the result of buffer underruns, which is more of a CPU/disk issue. As far as my Google-fu tells me, adjusting your audio buffer was disabled for some reason in Garageband 11. If you're using a version of Garageband older than 11, you can make your audio buffer a bit larger at the expense of latency. If you're running Garageband 11, you can lock tracks while you work, or render your instrument tracks and import them as audio files.
Why exactly would you need 9 tracks of Philharmonik? You are using all 16 MIDI channels per instance, right? It kinda sounds like you're only loading a single loop or sample set for each instance; even a complex piece would need maybe two or three instances of Philharmonik at most. It could also explain why you think Philharmonik "isn't even that great"; It's not top-shelf stuff like EWQL, but
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