Hello Rleff, to be honest, I've never heard the LS16 mk II. I have heard the LS16 mk I in my friends system with Krell amp and Dynaudio Contour 3.4 speakers and was pretty impressed. Overall though, I was not much of a fan of the older ARC preamps before the ARC Ref 3, which is still the best preamp I have ever owned. Yes, I know it cost a lot more, but IMHO ARC made a big jump with that series. Personally, with the older tube preamps, I prefer the VAC, BAT and Cary, though not necessarily in that order.
As for the 6H30 tube, it is very rugged and reliable, but there is not much to do in the way of tube rolling. This may be a good thing for someone just changing over from SS preamps though, as tube rolling can be time consuming and expensive. Yes, they do make what are called NOS 6H30 tubes, from the 80's and 90's, but IMHO the difference is not worth some of the ridiculous prices that I've seen being charged for them ($200-$300/tube). I've seen 6DJ8 variant's, 12AX7's and 12AU7's also selling for crazy prices, but IME I've heard more differences between these NOS tubes and current stock than I have between NOS 6H30's and current stock.
As a general rule (of course there are exceptions), I would say the 6H30 is rugged, reliable, powerful and dynamic. The old scholl preamp tubes (6DJ8, 12AX7, 12AU7) tend to have less of the above traits, but have better air, resolution and articulation, again IMHO, IMS.
Cheers,
John