How do I find out what firmaware and FS I need

im looking for APAC k800i firmware...
can i use R8AXXXX even if i hav R1GK?

Of course you can. Some people also call this "upgrading" :D

Read the XS++ 2.x tutorial, it's all described there.

another easy way to check is to use xs++
it is easier for newbies