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.
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.
While I agree that swapping out the oil caps is a bit extreme, and not something I would recommend or do (I would move on to another preamp, as Davemitchell suggests), I do know that quite a few have switched out the BAT coupling caps in the VK-75SE amplifier with Teflon VH caps, and have reported increased clarity and transparency. Some have even said that this cap change has more sonic benefits than changing tubes. Try contacting member Dgarretson, and/or search the archives.

Those teflon V-Caps do sound intriguing. AudioCap has teflon/tin foil caps as well. Same manufacturer as the MultiCaps I recommended. These caps are the creations of one Richard Marsh(the founder of Marsh Sound Design). If you know how good his electronics are: now you know part of the reason. One nice thing about tube gear- There aren't that many devices in the signal path(not really much to replace). Oh- the V-Caps take about 4 or 500 hrs to fully burn-in(so they say).