I would agree that the Parasound integrated would not be as good as the Hegel. The Parasound Integrated is nice and it's at a great cost point if you need an integrated with all those extra features (i.e. subwoofer crossover, phono preamp input, etc.), but it's not going to be as clean/clear as Hegel.
That being said, the Hegel is a very clean and articulate sounding integrated. I don't know how good of a computer system you have, but I would suggest listening to some youtube videos. Look for ones with Hegel H160 and others with Parasound A21. Though the Hegel is extremely clean and articulate, it's my opinion that it can be slightly on the sterile or artificial side (much like Bryston used to be with their SST2 and previous series).
In my own opinion and tastes, the A21 is a much more natural sounding amp, but still has the clean sound and attack/detail. However, it's a pure amp (not an integrated), so you'd have to use the Marantz full time for now. You can still add a preamp in the middle for doing preamp duties on dedicated 2-channel sources (i.e. external DAC, etc.).
It is true that an integrated or a preamp/amp will likely sound much better than the Marantz pre/pro. Even though the Marantz has discrete analog output stages, it likely uses op amps for the input stage of analog sources.
soix and I have slightly different preferences on how we would proceed in such a system. I would probably be going after the A21 amp first. He would suggest going integrated first. One thing to know here is the A21 does have a much larger power supply than the Hegel H160. With your speakers that will drop down 3 ohms in areas for the woofers, having a larger amp/power supply will help provide stronger midbass and bass body. Not that the Hegel would be bad at all, but I've found that the amp power supply does have some heft in this area.
A21 is just one amp suggestion. There are others, like you have said (Bryston, Anthem, etc.). All have their own sonic character that they bring.
