We have a JVC TV-DVD combo device, bought in Australia and labelled 'Region 4'. We note that it can play a Region 2 DVD (from Europe). Can we assume that if it plays Regions 2 and 4 it will play all region codes? We want to buy a DVD set from the US but are worried they won't work with our player. (Australia is closely linked politically, historically, legally with UK - but not so much with USA... so I worry that it may only have been unlocked for the additional UK region and not all regions.) Is there an unlock code for this TV/DVD player that we can try, if not? Thank you!