Upgrading good budget electronics that are working well can often be a frustrating business.
In theory both the amplifier setups you mention should be a step up, but it will be at considerable cost. Easy to get caught up in the hype, the Hegel in particular is very highly regarded at the moment and I rather like the Peachtree products on a personal level, (perhaps surprisingly) they have the 'bite' that I like when driven quite hard but are prety easygoing otherwise. In reality you are going to have to decide on whether the changes that you hear, whether from the Hegel or the Peachtree are real and important, not simply 'presentational'.
I have seen/heard the XDA in use and it is as transparent as anything at remotely competitive priceing though I believe the power amp to be a budget model. The trick here ti to try and set up some genuinely worthwhile auditions.
If you know your way around a multimeter, you can level match the amps by measuring the voltage at the speaker terminals, easy enough though the dealer will think you mad, such a comparison will tell you all you need to know.