apparently, a model can have a shield and an additional hand weapon if the army list selection allows it. the shield increases its save by 1 and the AHW grants teh extra attack special rule, like paired weapons, there is no exceptions for shields. RAW a model can use both at the same time... i checked the BRB and the errata, am i missing something?
"Page 91 – Two/Additional Hand Weapons Add “Requires Two Hands.” to the special rules on the profile."