Thank you very much ! Much appreciated.
OK, I just realised that I need to be a registered member for 2 months so I cannot actually download any files until then, and after posting 20 messages...
I have found the right firmware and the right custom pack to suit my phone and region. With the file system, It looks like there is on support on this site for the k810 - is that right ? The GDFS sections (bin / gdf / sbn) does not include any files for the k810. Do I need to upgrade the file system ?
I'll have to research the 'megabass' pack to see if it actually is worth trying to put onto the k810: the speaker isn't the best.