Benefit of Tube Dampers/Coolers on 6H30?

Overrated to who Jafox? Just because you don't hear a difference doesn't mean that a difference is not heard by someone else. Everyone's system is different. The only person you can speak for is yourself and how it may have sounded in your system!
There obviously must be a huge difference or folks wouldn't be talking about it.
That's the problem with this site, too many folks speaking their opinion as if it were a universally accepted fact.
This hobby is and has been about how a specific component sounds to that particular person in their system period and as I stated to Samhar if you haven't tried all of the different variations, then you can't speak from experience.

The claims of major differences with 6H30 tubes are way overrated.

I second that.

Eee3, I did not say I did not hear a 6H30 difference. I said the difference was minimal compared to the major differences between 6922/6DJ8 for which you related to. Please note again that I wrote "claims of major differences", and not, "claims of differences".

If you read the various ARC LS26 and Ref3 threads where people have written about differences with 6H30 tubes, you will see that the consensus there that the observed differences are minimal. Again, my comment was not of absolutes but rather a relative vs. differences between tubes of other types.

Compare an Amperex 6922 PQ or Telefunken 6DJ8 vs. the stock Sovtek 6922 in your ARC PH3SE. And then compare the 6H30 DR vs. common Sovtek 6H30 in your ARC LS25 II. You will then know the point I tried to make before.

Jafox, obviously you haven't read my other thread responses to this issue or you would know that I have and have tried every iteration of the 6h30 that's out there. To include: Sovtek, electro harmonix,Bat technology and the Nos 6h30-dr's. (I haven't had sovteks in my LS-25 in over 3yrs.)
I just recently compared a new pair of electro harmonix 6h30pi gold pins(100hrs. burn-in)to a 5year old pair of Bat 6h30's and the bat's are still considerably better! not minimally better. The 6h30-dr's the same result.
I have a audiophile buddy who has an LS-26 and his experience is the same. In fact he just purchased 2 more pairs of 6h30-dr's he will tell you the same thing.(sum4jn@sbcglobal.net)
Also, I've not had sovteks in my PH-3se since I purchased it 5 yrs. ago. but I have had in it Amperex 7308PQ's 6h23n Russian, matsushita 6dj8's,amperex orange globe 6dj8(mid 1960 vintage) and currently siemens-halski 6dj8's, so I've made the comparisons you are talking about.
I am not a novice, I've been in this hobby 25 plus yrs. and speak from experience not from what I've read or heard from someone else. And as far as your point about the threads on the LS-26& Ref 3, I'd be willing to bet(an I'm not a betting man)that the majority of the folks only compared sovteks to electro harmonix 6h30's (just as Samhar did) an in that regard they're right the difference is only minimal.
Finally, the 6h30-dr's are currently selling for $250-$310 pr. as are the amperex 6922 PQ's an the telefunken's(to use your comparison) and the siemen's for even more. So, my question is if they're not considerably better, why are folks buying and selling them for that price?
I certainly wouldn't pay that price for a minimal difference!

Anything new or old to share about the CDP's?