Tubes combination

I own a pre BAT VK 51SE, amp VK 75SE, Sonus Faber Cremonas, Sim Audio CD player, Cardas interconects, Kimber speaker cables. The sound of this system seem's pretty good to me but I wonder I could get more resolution/detail with a diferent combination of tubes in the amp. I'm using Electro Harmonix 6SN7 EH and 6V6 EH tubes on the amp. May I have your opinions on this please?

I haven't heard the EH 6SN7s but IME you can get very convincing improvements when you go NOS with this tube. However the 6SN7 is one of the more sought-after old-stock varieties and is expensive in consequence. And again in my experience, the improvement brought by premium NOS has been in the realms of timbre, balance and extension more than in detail and resolution. Others may have different things to say, though.