Tyres for 4WDing

I am looking at getting some wider wheels for my S3, and was wondering if anyone has had any probs with sunraysia wheels. I currently have the original r15 on her but I am trying to do more beach driving than anything else, so the wider the better. The ones I am looking at are R15x10. However, the bloke who is selling them has 2 road type treads for the front and 2 more mud like tyres for the back. My old man reckons I should probably have all the tryes the same, otherwise I will bugger the transfer box when I am four wheel driving. Is this a problem does anyone know?
thanks heaps,
Dick