Dynaco Pas 4 Pre-amp tube questions

I am looking for any current or former Dynaco Pas 4 pre amp owners who can help me with a couple of questions. I would like to replace the 6922s in the line stage. I was thinking about going with Sovtek or Electro Harmonix. I have seen these tubes on sale and they usually say "preamp quality", what does that mean? If I play my stereo an average of 7 hours a week, how long would an average 6922 tube last? Also, I will not be using the phono stage on this pre-amp, can I take out those tubes without doing any harm to the operation of the unit? Thanks! Vlad