Ianrmack, I just got a set of six NOS input tubes for my Berning 270 - I bought ones that are 1% matched, and the four 12AT7's are cryo treated. I highly recommend it. I just installed them Friday and my initial impressions are this: more presence (almost holographic), more detail, more air around the instruments, better bass, and just an overall better, more pleasing sound - and it is still improving. Right now I am using ML SL3's, which are not great in the bass department, and after installing these tubes, for the first time I am getting musical bass. For example, on well recorded small jazz ensembles, I can easily tell that it is an acoustic bass resonating and not an electric bass. Before, you had to listen very closely to tell the difference (although it did get better when I switched from my ss amp to the stock Berning).
I also am experimenting with going directly to the amp from my cdp and tt. So far, I like it better, but I am bypassing an Adcom GFP 750, which is undoubtedly not as good as your Hovland. I may go back to it if I miss the remote volume control too much - the 750 in passive mode does not do much to the signal - probably the extra set of ic's has more of an effect. Your comment on the soundstage difference is interesting - a friend of mine really believes in the value of a good preamp and you have one of the best.
Congrats on your Merlins. I have not heard them but others say they are a great match for the Berning. (I have a pair of AP Avantis on order and am anxious to hear how the Berning matches with them - it did very well with their little brothers, the Virgos.)
Give us a report on how the Merlins + Berning sound after they are broken in, and try some NOS tubes - you won't regret it.
Cheers
David