I have either Kuwaiti Dinar (1 KD = 2,83€) or Omani Rial (1 OMR = 2,25€) in which both are of high value. However will money changers in Europe accept that for Euros. For example: the highest bill from Oman is 50 Rials (112€) & from Kuwait is 20 KD (56€).
Of course, currencies from the Gulf are petro states (like Kuwait) have higher exchange rates. Should I bring those currencies into Europe or convert it (for USD) prior to travel? Also, will I be able to bring 6000 KD (16,960€) in cash?


There’s not a lot of places accepting those currencies. Either take a European currency or US$.
But better to not take cash at all, especially that much. You have to declare it etc. Just pay by card and use ATMs if you really need cash.