2Kemon
Sorry for the late reply, I seemed to have missed your post.
Both Infinite and Xstream are stand alone, the difference is Xstream can integrate with Maya, C4D and Max using other render engines like mentalray, vray, etc.
IMO you do not need any of them as the 'Complet' version has all the bells and whistles needed.
As for integration with SU, Vue 7 can import native SU files so you do not require SU pro to use it, however Vue does not recognise your groups and component structures so having models with hundreds of identical components in SU may seem light but as soon as it gets imported into Vue the all become unique groups which can explode into one huge taxing model, fortunately Vue can handle billions of poly's unlike SU.