Other than a good audio-source and signal path, nothing is *needed*. I mean, feel free to run it through a tube preamp with tone control to get your personal flavor or what have you, but the important part is having a clean strong signal. Clean signal means a DAC/preamp/phono amp cabled up with good shielded RCA.
You can roll the tubes to get subjectively better sound. The 6ZH1P preamp/input tubes (the small ones) are easily replaced and will give the most sonic changes or gains. I suggest the (subjectively) cheaply priced and quite readily available GE 5654W and Voskhod 6ZH1P-EV. Whichever you pick, you want them as a matched pair or you will get channel imbalances. I personally use Voskhod 6ZH1P-EV date coded 1984 and couldn't be happier.
The 6N24P power tubes are a bit more difficult and won't give that much of a sound gain. You can find 6N24P very easily for very cheap ($1-3 per), quality ECC89 or 6FC7 are a bit more difficult and likely expensive. I suggest not rolling them unless you've got a failure or reeeeeeallllly think that annoying buzzing is actually coming from the tube (protip: it probably isn't; either your cans are too sensitive and giving the tube hummmmm, your mains are dirty and you need a power filter or UPS on your audio stack, or you've got massive EM interference nearby and should try moving the amp away from wireless gear (phones included)).
But seriously, it is your toy to play with. :)