The 20.3 is more nearly comparable to the 608/609, while the 708/709 would be comparable to the 40.2. There's no good reason to believe that Integra models are in reality better in craftmanship than the corresponding Onkyos; they're designed and manufactured by the same people.

Yes, MultEQ is a significant step-up in the accuracy of equalization, especially in the low bass frequencies,so in my view going up to the 700 series in Onkyo(or 40 series in Integra)is very worthwhile.

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Enjoy the music, not the equipment.