The G system is definitely a well-design piece of kit, but if you're a total tweakhead or are looking for some completely outrageous effects, it's just not going to cut it 100%. MIDI pedalboards exist that can work with any processor, including a Harmonizer.
Rocktron, Voodoo Lab, and Custom Audio Electronics are just a few manufacturers with such products. The best part about the custom boards is that most of them are 'macro' triggers, meaning you can send multiple MIDI commands to multiple devices with one press.
HTH,
~Phil
