PS3 and Onkyo TX SR-606

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Ok, so - I'm torn between the 606 and 706.

Does the 606 have any kind of feature that enhances the sound at low levels?

I've heard that the 706 had THX Ultra (basically, when the sound is turned down it enhances the surrounds and bass so you still get a "full" sound.) However, I also heard you can use the Audessy EQ - does the 606 have this?

Thanks,

EDIT: What's the difference between Audyssey Multi EQ and Audyssey 2 EQ????