The Onkyo system is great as it is (hence being a two-time Award winner!) but can support better speakers than those it's supplied with. However, i'm not sure of the specs of your Ruarks, to judge whether it'd be happy with driving them.
I'd be inclined to buy the excellent system unit, give it a try, and then if it doesn't pan out with the Ruarks to buy some Tannoy Mercury F1 Customs for £110 or Wharfedale Diamond 9.1s (available for £130) - you wouldn't have spent much more then than if you'd bought the full Onkyo system, and you'd have an upgraded sound.