They have the possibility of having more power, as external amps often have more power than AVR amplifiers.
In this case, speaking of amplifier power only, there might be an improvement but the value isn't that good. $2400 is a lot to pay for an amplifier when you could goto Outlaw audio, order a Marantz pre processor combo with one of their own amps for under $3000.
The package with the 72000 gets you a very heavy amplifier, which is a downside. But it will do 200x7 watts into 8 ohms, and 300x7 watts into 4 ohms. That is some crazy overpowered amplifier, for much cheaper. Of course the Marantz amp is prettier
And the Outlaw is 90 pounds which I would not personally want.
They don't seem to have a package deal for this, but you could also look at the preproc paired with the more reasonable 7125. Now, the 7125 is only 125 vs the Marantz's 150. But that is not a relevant difference in power. Into 4 ohms, the 7125 does 190 watts which is very impressive for a $1000 seven channel amplifier. I would bet some money it can outperform the Denon and have similar performance to the Marantz. In fact, I am not sure there's a better seven channel amplifier for that price anywhere. Were I in the market for separates and did not want to pay $5000 or so, I would look at something like that.
That all being said, your Denon is likely more than adequate for your needs. I don't automatically assume separates must be better and that Denon looks very powerful. If it can't adequately drive your speakers for some reason than perhaps there's some improvement with a better amplifier. It's possible the Marantz pre processor is better in some ways, but without a lot more research it seems a bit of a lateral move to trade the Denon for the Marantz pre proc plus amp.
One option is to keep the Denon, as long as it does everything you want and add an amplifier to the Denon. You likely need to add a power one. You could look at Emotiva amplifiers but they lack a powerful 7 channel amp. You could amp 5 channels externally, and use the Denon for 2 surround channels. You could also look at various Outlaw models.
You may know this, but on paper small differences in power don't make too much of a difference. So you end up looking into amps with double your current power. However an amp that's not twice the 8 ohm power, might have such good performance into 4 ohm loads that it could make a difference. AVRs are not known for their performance with 4 ohm speakers. You can also take a guess that a competent external amp that has excellent 4 ohm performance can better cope with difficult speakers. It's possible for the impedance of speakers to dip down towards 2 ohms which is why it's an interesting question. Would I take an external amp like the Outlaw 7125, which while it only puts out 125 watts of power into 8 ohms, puts out an impressive 190 into 4 ohms? I think I might IF I was in the market for an external amp in the $1000 range. I don't know that Yamaha's top of the line model can match it, and even it if could you could use both the Yamaha and the external amp in interesting ways. It's a bit of a dilemma as the top of the line Yamaha is very power regardless of what some people think.
One more thought. Those Outlaw amps are spec'd with all channels driven. That likely means they can put out some impressive dynamic power for transient peaks. As AVRs are typically spec'd with two channels driven, it's a bit like apples and oranges to directly compare the 7125 to a receiver.