I found something that maybe of interest to you.
I found the manual for the Ricco U80 here:
http://www.riccodigital.co.uk/downloads/ainol/u80.pdf
Then I followed the link in that manual to their website for the
U80 product and it mentions "
MicroSD Card Expandable to 8GB".
So it should take 8GB, but it maybe a specific MicroSD card you need to get for it or it needs to be formatted in a particular format for it to work.
You could try to contact them on their website to see if they could give you some pointers.
Sorry, I don't have this player so can't give you the exact answers. Hopefully that's pointed you in the right direction.
If you do find the answer, can you please post it here on the site? Would be good to share this information for other people who may ask the same question later.