ARC LS15 tube replacement suggestions

I recently purchased an ARC LS15 line stage to run with my ARC VT100 mkIII amp.  Everything sounds great but I have no idea how old the tubes in the line stage have been in there, so I would like to change them out.  Audio Research suggests the EH tubes they stock at the factory.  I have friends telling to go NOS and I have reached out to a couple of dealers, and they wouldn't really make a suggestion.  I know there are some folks on here that either have or have owned the LS15 that can give me some feedback.  Thank you!