I've tried Guitar Rig II. It sounds great but it requires a powerful computer with a great sound card.It's good for recording,can get very similar sound as your Idol has.
Here can find more information about Guitar Rig II:
http://www.native-instruments.com/in...=guitarrig2_us
Exist also without foot controller GRII:
http://www.native-instruments.com/in...itarrig2swe_us