Reading over the manual clears up quite a bit. It should answer these popular questions. Let me summarize here with some Cliff Notes:
1. How does it sound compared to the actual IIC+?
Well, after trying out a lot of IIC+ amps for comparison, it's actually modeled after what they consider the "holy grail" of actual IIC+ amps (best sounding one in their opinion), down to the last components. All EQ models have a one cap difference (larger, slower signal, fatter) to the non-EQ models (less sub-lows, tighter, more urgent). The V's IIC+ can use the EQ, but uses the smaller cap of the non-EQ model.
What does that mean? It means that the IIC+ in the V actually has a faster, tighter attack than original IIC+'s w/EQ's and you can add more bass (because of the lack of sub-lows) without it getting flubby. So to answer...how does the IIC+ mode sound compared to a real EQ model IIC+? Faster, tighter, and more urgent... :wink:
2. Is the Extreme Mode really just a Mark IV with the Presence knob pushed in?
No. It's based on that, but taken even further. According to Boogie, it's voiced almost the opposite of the Mark IV mode on the V. It has the most gain, it's aggressive, forward, and has "stop on a dime" dynamics. It's also the loudest due to the change in negative feedback in the power amp, which seems more extreme by description than what happens in the Mark IV. for those who played this mode and thought it sounded "Recto-ish," it's likely because the power section starts looking more similar to the Rectos Red mode. Not that it will make it sound like a Recto, but the similar feature will definitely lend itself to being more modern.
So rest assured, Extreme is a LOT more than just a Mark IV with the Presence pushed in.