Don't trust what vendors say or their prices. The stock tubes on Parts conextion 3910 are mediocre. Try the Mullard it will be an improvement but I agree with Dennis's comments. I run a set of affordable Siemans 6Dj8 from VTS tubes in my 3910 and they are fantastic. And yes I did have the upper bass problem you mention, until I tube rolled. One other thing to consider is that if this is a big source improvement for you do not discount the idea of having to re-position your speakers. You may have placed you speakers to make up for source problems, ie weak bass.
