a friend of mine bought the synergy system. i think he got like a fender deluxe and a friedman smallbox module (or whatever is closest to those). i sold the Egnater module system when i managed a music store, so i'm familiar with that too. they seem very similar, if not the same thing.
my friend brought his synergy 2 module rack, and i had my AX8 on this gig. granted he didn't have it too long to dial it in perfectly or whatever, but you could clearly hear the difference and the synergy system sounded like the "typical modeling sound" that people associate with modelers.
i think the weakness is in the real lack of IR capability. probably some generic cab sim for the direct outs. it just doesn't do it justice at all. the AX8 sounded full and rich, where his had that hollow, prickly high-end, no definition sound. it works, and especially if not comparing to something. but he was a little disappointed.
that said, he used it at his own gig the next day and he told me it sounded great there. so he's happy, and it works for what he needs. he usually uses a real Smallbox combo, but this gig was too small for it.
but directly comparing it to my AX8, the difference was pretty substantial. i don't even tweak my presets very long or very detailed. just basic bass mid treb and the GEQ for the most part. it's the fundamental modeling approach that is really different. and i think an IR system would make it sound so much better.