The more important specification for the amp, in terms of suiting the Sopra, is how much current it can generate. As a rough guide, whichever amp gets closest to doubling its power rating into 4 ohms will be better at providing the current needed to suit the Sopra. Most likely, it would be the Aragon. If for no other reason than most multi-channel power amps share one power transformer across all channels. So try using the Aragon just for the Sopra ( so 2 channels only). I have not heard an Aragon amp for many years, but my recollection was they were a bit harsh in the treble, which the Sopra is not going to hide. If so, try the Marantz. I'd prefer to put up with softer bass than a screeching top end.
I suspect when you are listening to 2 channel music, you may prefer listening to the system running Pure/Direct rather than using the DSP section of the Marantz pre/pro which will be doing the crossover. This should just send the stereo signal to the Sopras in full range, with no bass management, no delays, etc etc. But I don't know how the Marantz can be configured.
So the crossover point for the mains (FL and FR) is only an issue for surround sound/AV duties. As I said in the earlier post, Audyssey would prefer you to set everything to 80Hz, because that is optimum for the Audyssey filters. What will work best will depend on the characteristics of your room, speaker positioning (particularly FL, FR and sub) etc. So just try different settings - although you may get sick of running the Audyssey optimisation after the first 10 times. I would not go below 60Hz myself, and suggest you don't go above 80Hz.
For future system development, you have it the wrong way around. The AV system hangs off your music system. There is no point looping a preamplifier out of your Marantz then back into it. Even with the World's Best Preamplifier, the sound could only get worse, not better.
The high quality stereo preamplifier you proposed would be connected to whatever power amplifier was running the Sopra. The Marantz AV PrePro would connect to an AV bypass input on the new stereo preamplifier: an AV bypass input means that it bypasses the volume control of the preamplifier, so you can use this input when you want to listen to your surround sound setup.
When listening to music, your sources should be connected to an input on the new preamplifier. If your sources, such as a DVD/Blueray, don't have a decent analog output (i.e. their DACs are not as good as, or no better than the Marantz), then there is simply no point in buying a separate preamplifier at this stage.
You have bought quite high end speakers, using all your available funds (and perhaps even more!!) on the basis that it is something you can grow into over the long term. Makes sense to me, as speakers that are good, are always good. But I think you need to make a plan on how you will evolve the system, and I would strongly suggest this order:
- A 2 channel power amp that is capable of achieving the transparency and dynamics that the Sopra are capable of. As per my earlier comments. Alternative is a very high level integrated amplifier - only because a decent preamplifier is an expensive component, and shackling a good power amp (and the Sopras) to an average preamplifier is a waste of money.
- A decent preamplifier - something like a Wyred4Sound STP-SE would be the absolute minimum to potentially offer any real improvement over the Marantz.
- A decent source for music, most likely to be a DAC.
Enjoy the journey!