Tubes for Rogue 99

I'm in the process of buying a Rogue 99 preamp that is equipped with the stock tubes. If I want to upgrade to some NOS tubes do I have to replace all 4 tubes with NOS tubes?
Any suggestions on the what type of tubes is also appreciated. Thanks.
Call Mark at Rogue, he'll tell you exactly what you need to know.
Good advice from Finfinder. Mark is also very responsive to email. If you phone however you can place an order for upgrade tubes from Rogue at very reasonable prices.