I just recently jumped on the Synergy train a few weeks ago and have so far played/own the Uberschall, Fryette UL and IICP modules. These things sound fkn awesome. Disclaimer...you will get different results going straight from SYN-1 or SYN-2 to your computer Vs. plugging into a power amp or amp FX loop to cab. No surprises there I suppose. I suggest getting a dedicated power amp for more consistency. The modules respond differently to the amp you are plugging it into, which also, is to be expected. This is all for the feel and frequency response.
As for the tone of the preamp, these things get REALLY close.
Bogner: I own a rev blue currently and have owned a TJ, which the module is based off of. The character and voicing are dead nuts but the eq response is off as well as the amount of gain available. Way too much compared to the real deal counterparts.
Fryette UL: I've owned quite a few different versions of these amps and know it very well. Steve Fryette nailed this module. My only complaint is no matter what amp FX loop I plugged it into, it was just too bright overall, especially against the real deal amp. The highs and presence were overbearing. However through my friend's Fryette 2/90/2 power amp (which I need one now for myself LOL) it tamed it down and got MUCH closer. It was all there...The feel, the bark, tightness, aggressive high end sparkle was all intact. This is the module that made me a true believer in the Synergy system no doubt.
IICP: I've owned a couple of MKIII's but never a IIC+. I have a friend who had a real one and spent a weekend with it. Does not make me a Mark expert. But this module is badass. Super tight and aggressive. More dry than my MKIII red and blue stripes I've owned however. Also sounds more hifi. Others say more modern and maybe that's the right description but again, I can't 100% accurately compare to a real IIC+. I'm honestly basing the tone more off of the III's I've owned.