Arsh,
Dan Meinwald, the EAR USA rep, uses one Amperex 7308 and one Mullard (all New Old Stock tubes) in his EAR Acute. His stuff always sounds great and is highly regarded in the audio industry, even from non EAR dealers I've spoken to. That may be a good starting point. I personally like that sound but would like to get a bit more sound extension based on other system component. Your listening tastes and other system components should also be considered when deciding which tubes to put in. Dan Meinwald thought putting 2 amperex tubes would be too lively, but my system is already warm and laid back with my Primaluna EL34s and Sonus Faber Olympica speakers. A little more liveliness and soundstage with some warmth is where i need to go.
If you go on other forums and reviews, many have put the Siemens in the EAR Acute and loved it. I read one review on Upscale Audio of a reviewer loving the Telefunken 6922's. On reviewer positive feedback put in Ediswan, while another reviewer put in Mullards. there really isn't a right or wrong. It comes down to your tastes, genres of music you listen to, and other components of where it lends and what you are trying to do.
The one thing I'm not yet sure of is how changing some tubes of my Primaluna Integrated Amp will impact the sound of the EAR Acute. I've only tube rolled the EAR Acute thus far. Not sure what substituting some 12au7 NOS tubes on my Primaluna preamp section will do with the EAR Acute hooked up to it. If the Amperex's are good overall, but could use a bit more clarity, maybe a more transparent 12au7 tube would be the way to go. How big of an impact will that make to a CD player hooked up to it, I have no idea. Any body ever do this in a similar situation? What effect did changing amp or preamp tubes make as to change tubes out in the actual source CD?