Extreme Midrange Bloom

Hello: I'm using a BAT VK52SE with the 6H30DR tubes recommended by several folks here on the Gon. I've noticed an extreme emphasis in the upper midrange frequencies which is somewhat unsettling and in fact causes an almost artificial honking presentation. Is this simply the BAT house sound or is there something I can do to resolve this anomaly? I've never experienced this in any other preamp I've owned in the past. I love the build and general fit and finish of this preamp. The user interface is excellent. An audio enthusiast friend suggested this could possibly be a result of the oil filled caps BAT is using. Any help would be most welcome since the pre is great in every other way. Accurate bass, sweet highs and a very unfortunate bloated midrange.
If you know what to listen for, and thrill to the sound of live music in a real venue: nothing beats tubes. Any equipment(tube or SS) takes time to sound it's best. Taking the time to burn in gear, and taste various tubes, is an act of love for some of us. Skydivers(I) have a saying: "We that dance are considered crazy by those that can't hear the music." Harley riders(I) have another: "If I have to explain- You wouldn't understand." Oil-filled caps will usually have somewhat of a fuller, rounder midrange(ala Mullard tubes, for instance- which some like), than would most film/foil caps(polypropylene/copper foil probably being the other extreme). I'm not certain about the burn-in time.
All, let us keep this little thread on the narrow topic at hand. . . . if oil caps were imparting a slight unwanted richness to the upper mids of the 52SE, is it practical to change them, and what caps should be used without overcompensating?
I don't know why you want to change out the oil caps. If you don't like them, you shouldn't buy the 52SE. You pay a lot of money for the Super-Pack.
In my experience the BAT tube gear sounds very tubey and bloomy and that is what some listeners prefer about them. Also, BAT has for years offered the NOS variant tubes you are referring to as a desirable upgrade option.

My experience with those tubes suggests that they indeed may make the sound even more rich than the stock leaner sounding Sovetek 6H30's, pushing the already tubey house sound even further in that direction.

If you are looking for more neutral sound try an ARC or VTL piece instead. Otherwise returning to the Sovtek tubes will at least cause the sound to head in the other direction.
Tweeking equipment is not very difficult, and can yield outstanding results when applied to an already good piece of gear. I've used the MultiCap film and foil polystyrenes, and auriCAPs to excellent result(very transparent). Always buy in 2% matched pairs, watch the voltage ratings, and be certain to orient with the outer foil lead end toward the load(auriCAP leads are color coded). Again- I'd never recommend anything be changed until one knows beyond doubt the equipment's sound after burn-in. Often it just takes an interconnect/cable change to eliminate colorations.