So I have some personal experience with the speakers you are using.
(702s are the bi-pole surrounds, the 703s are the bookshelf speakers and the 706 is the larger of their 2 centers...towers are the 705s which I have and the 707s. The second center is the 704).
Anyway, the 705s sound "fine" on receiver level power. But they will really open up with good, high current amplifier power. Remember, not all watts are the same. And almost all AVRs lose a considerable amount of power as you add speakers. You have one shared power supply that not only has to provide power to your amplifier boards but also has to handle the processing portion as well.
Going from 2 to 5 speakers, most AVRs will be down 50% or more power from their 1 or 2 channels driven rating you see in their spec sheets.
Even off-loading the front mains or even all 3 fronts will gain you a considerable amount of amplifier overhead. Your transients will be smoother and cleaner and the internal amps won't run out of gas so quickly when all they have to do is provide power to surrounds.
I have a Marantz AVR and a Marantz pre/pro with external amps that I would happily A/B for you to show you the difference even on high efficiency speakers (my theater's JTR Triple 8s).