I know it doesn't really help you much, but i love that mp3!
Right, my experience (i do a lot of melodic death metal and also have a band with a keyboard player (fast folky metal), so while no expert, i have some experience)
The question i must ask you... Do you want your piano to sound real or Synthy?
I.e, Real (adagio, sympony x) or synthy like Dimmu borgir.
I always start by Setting an EQ cut in the low frequencies so no piano sound conflicts with the bass or the kick.
With strings, a boost around 14khz gives a nice "air" to them.
I've also found, if dealing with instruments that have a wide dynamic range (piano, strings) etc. In a metal mix. Compress them to hell.