The simple answer to your question is that you can only do this, if you have access to a KN5000.
If KN5000 Style files have been saved as '.RCM' files, ie as a single load of 20 Custom styles, the KN6000/6500/7000 will NOT recognise this file. These keyboards use a '.CST' file for this purpose and the two are not compatible. However, if the KN5000 style files have been saved individually in '.CMP' format, they should load OK in to the KN6000/6500/7000.
The only way around this problem, is to copy all the files in the KN5000 Custom memory to Composer and then save them to floppy disc, but of course you need a KN5000 to do this and it's quite a long process.
If anyone is considering upgrading from KN5000 to KN6000/6500/7000 and have any of your own styles or commercial style discs, which are in '.RCM' format, then if you wish to retain them for use on the KN6000/6500/7000, convert them to '.CMP' format, before parting with your KN5000.
After silence, that which comes nearest to expressing the inexpressible is Music.