The History Behind Viva Linea?

Can anyone here share a high-level progression of advancements in the Viva Linea preamp? In searching for a DHT preamp, this one came to my attention, and literature around it has been minimal at best, but it’s reputation seems to be stellar. 
Research has led me to find that it has gone through many iterations in the last 20 years.

Viva Linea 300 - one of the originals where the power supply was in a big V-shaped chassis

Viva Linea XP - from my understanding the next version. Later models shifted away from the V-shaped chassis

Viva Linea (current model) - newest line in slimmer chassis

Each of these models seemed to vary in power tube configuration - some built in 300B, others in 2A3 or 45. 
Is there anyone that can tell me what is different technically and sonically between these models? I’ve seen some of the first two generations sold at relatively affordable prices so more than anything I’m looking to compare between the first two models and between the XP and the current model. 
I have contacted Viva directly, who guided me to talk with dealers, and none of the dealers I’ve spoken with seem to have the historical understanding of this model.