Al, I am currently listening to the Forests powered by the PrimaLuna Prologue Two, and am pleasantly surprised at how well the Two powers the Forests. Many say these need 200W+ to open up, but with tube power I think you can get by with less.
I heard the Forests powered by the Krell kav400xi at a local dealer and was impressed. I brought one home to hear the differences compared with the PrimaLuna. The Krell did open some things up in terms of transparency. The imaging was a little tighter and the tonal accuracy of instruments was more accurate. The upper registers of female vocals could become fatiguing after long listening sessions at high volumes.
Having said all that, the PrimaLuna was simply more emotionally involving IMO - and that is the most important thing to me. The bass was surprisingly more present with the PrimaLuna. The bass was so tight on the Krell that it was almost non-existent? There is some added 'bloom' to vocals on the PrimaLuna compared to the Krell, and in that I mean they seemed a little exaggerated in size, not in colorization. Female vocals are sublime!
The PrimaLuna was just easier to sit back and enjoy the music with. I found myself over analyzing the presentation with the Krell too often. The PrimaLuna was simply more enjoyable and sucked me into the music.
Hearing some of the benefits of added power with the Krell, a more powerful tube amplifier would probably only add more of a good thing. PrimaLuna is releasing monoblocks (rated at 60-70WPC?) in the near future and I think these would make a great pairing as well.
I did contact Totem, and they recommended the Audio Research vsi55. I also inquired about the BAT vk55 (as I am now a fan of the autobiasing feature) and Totem said that it should mate well. I could live happily ever after with the PrimaLuna Prologue Two, but I have to be honest that I am curious to see what a little more in terms of tube power will bring to the table. I am most looking forward to the Prologue monoblocks.