@PENG - I wish it was easy as simply changing Amp Assign and moving on your merry way. But with the 4700 that is not the case. Maybe it's different with your receiver?
Here's why:
My normal setup is shown below. Fronts, surrounds, rear surrounds and front highs. There is no option in Audyssey to use front pre-outs in this configuration.
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So I take your advice and I open "Amp assign" and switch Height speakers to front and rear. This enables the option for Front pre-outs. It's odd that I have to add 10 speakers just to get this option but I do it to work around the Denon 4700 design.
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Then guess what happens? Audyssey is now greyed out on the monitor and not available. All the EQ is gone and Dynamic EQ is turned off. Audyssey says I can't access this menu until I run Audyssey again.
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As you can see, you cannot maintain your settings when you move to a different "Amp Assign" setting. As a test, I go back to "Amp assign" and select Pre-amp mode. Once again all EQ settings are lost and Audyssey menu items is greyed out and Dynamic EQ is off.
Next, I move the Amp assign back to my original configuration. Only then is the Audyssey menu item available and Dynamic EQ restored. There is NO provision in the 4700 to change amp assign modes without completely re-running the entire 15-20 minute Audyssey setup confirmation with the Mic inserted.
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And if you want preamp mode, you will need to run an Audyssey setup for that and save it so you can switch to it. The 4700 software is not designed to make it easy to change amp assign modes without a complete redo of Audyssey.
Maybe you have not done this? Or your older Denon is different? You really have to stay with the amp assign mode you originally configured or be willing to start the setup all over again.