NOS tubes for Aesthetix Calypso

I recently purchased an Aesthetix Calypso. I really like the preamp, however I would like to purchase some NOS tubes for the unit. First priority would be a liquid smooth midrange, second would be soundstaging, third would be frequency extension. I would really appreciate some Calypso owners offering up some experience and suggestions with the NOS tubes. I would also like advice on where to purchase NOS tubes. My system consists of Maggie 3.6r's, 2 Vandersteen 2WQ subs, A SMC modded McCormack DNA-2, Resolution Audio Opus21 cdp, and all Purist Audio cabling. Thank you in advance for all your help.

rhythmace4218