congratulations on your 7600 and welcome to the forums!
The preamped presets have their input level patched to External 1, which in turn is assigned to HIGH. This means you should get sound from them as soon as they are loaded.
My advice is to execute a full reinit of the unit by powering it and pressing and holding the 8 key when you see "H7600" on the display. The next step is answering "yes" to the question you will see.
Please let me know how it goes….