I can't answer your question but can offer you some thoughts. I've rolled tubes in a lot of high end gear over the years. While you can generally describe the attributes of a particular tube by type, brand, place of manufacture and year date, to me, much has to do with the overall voicing of the system and what complements it. So, taking a given tube in isolation, no matter the vintage or rarity, will not be a complete answer. I think you have to hear the tubes in situ in your system.
I never owned the unit you have- I had older ARC stuff, dating back to the SP-3-a-1 and stopped at the SP 10 mk ii (which did use the 6dj8). The problem I found in the SP-10 was that it was highly microphonic-- sort of known for that. It had a sweet phono section.
I gather that the later ARC preamps eventually switched to the 6h30. While BAT and a few others originally used the old DR Reflector, that tube is now very hard to source, especially early stock. The modern iteration of the 6h30 in my particular line stage- a Veloce Lithio 2.0-- does not have the mojo of the old DR tubes. I did source a matched quad NIB a few years ago that was dated from the late '70s.
I gather that with more modern ARC gear using the 6h30, the effect of current production (Sovtek or EH) is not as dramatic; that is, the DR variant may not be necessary, but that's a question I'd ask if you are considering a later ARC product.
I've pretty much stuck with older tubes, though they are pricier than ever and harder to find as true NIB, never used tubes. I think you'll find more alternatives in 6dj8 land than in 6h30 land, especially if you are willing to try older tubes. My only advice is to buy from a reliable supplier.
I'll let the current ARC tube owners chime in on their experience with the 6h30.
