Use the native codec DVCProHD 720p50 or 25, depending which you shot. Are you importing P2 or from a Firestore? Edit in the codec and Master to whatever you need i.e. drop the final version into an umcompressed HD timeline and play out to file or tape from there.
Just drop a clip from the HVX into your final cut timeline. As long as you have your prefs configured, FCP 6 will ask you (or automatically) match the sequence settings to your clip settings. I was recently asking myself the same question with HVX footage.
"Never underestimate a kick to the nuts"
Bas Rutten