Anyone heard Underwood level1 3910 mod?

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.

forgot to recommend you search for "Joe's Tube Lore" lots of good info

It appears that I have spoken too soon. My disdain for this mod has evaporated. The Mullard tubes with some burn-in time has produced a really terrific CD player. Extremely listenable with great presence. Perhaps a little warmer than the Benchmark, but it doesn't send me out of the room like the Benchmark. Thanks to all for the tube advice - especially Dsremer and Nickturner920. I'm going to call VTS today and order a pair of Siemans tubes. (Although the sweetness of these Mullards is hard to resist).