Hey Kev, you're not getting much help here are you? I am in the proccess of listening to both of the entry level siblings from BAT and Sonic Frontiers. The VK-3i and the Line 1 both in stock form as far as tubes go. I am having a very hard time choosing one over the other! My power amp is the VK-200 driving Thiel CS3.6's, and I know that is not what you were asking about as far as the amp match-up is concerned but this is the judge and jury in my living room system. My reference guide is my main rig in "The Addition" or as my wife calls it "The Crypt". Very high resolution system to me...all Krell, KRC-HR pre, MDA-500 mono's, MD-20 transport w/ Reference 64x dac, running all balanced.
The Line 1 has outstanding features and function to start. The sound does seem a bit lean to me at times but never fails to convey the entire musical "detail" on the recording. It does seem to have a clean presentation without any tube characteristics at all. Upper registers on up to the limits of my hearing are very detailed and open, different types of cymbals are very distinct. Mid-band feels somewhat cool to me, female vocals and violin/viola duets are very cleanly reproduced(lots of detail) but do not give me the warmth of the real thing. Bass is good to excellent in pitch/timbre/tone, attack and release. The Line 1 with stock 6922's does seem lean and clean with a good amount of detail, and from what I'm told tube rolling will make a big difference.
The Bat VK-3i is a whole different story for me. While not being the last word in resolution it HAS showed what people mean by musical and emotional. I have spent my time and money on resolution of information for the greatest of detail,(that's the musician in me) hence the Krell system. As I get older I have come to appreciate the passion and emotion of a performance. That is where the VK-3i has put me in my place. Some of the inner most details of the recording are hard to hear at times, not to say inaudible but not as well defined(detailed) as the Line 1 BUT,,,BIG BUT,,,the ebb and flow of the VK-3i has won a place in my heart and the heart has convinced the head that it's OK not to have too much detail. I do not find it to be dark at all but do notice the upper octaves don't tell me "as often" which cymbal is being used as clearly as the Line 1 or the KRC-HR. Which, by the way, is very hard to hear at a live performance. This to me is a VERY MUSICAL pre-amp. Vocals make me melt and strings have the body I've heard live.
It's been a tough battle here, Analytical vs. Musical Putting each under one heading...Analytical / Line 1...Musical / VK-3i
I hope this helps, if you have any specific questions feel free to email me.