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. 
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I can't shed any light on the model history but I will say this, if Viva can't/won't answer these questions and nor can their dealers what does it say about Viva's customer service? This market is too small to treat potential customers that way, Viva should be glad to share the info and tell you why the current iteration of their preamp is best.

Also I remember a past thread here about Viva refusing to repair their products bought on the used market.  Do some research for past threads on here.
Thanks @jond yes I have done my research on this thread and have seen the one you mention. I’m not expecting much service from them, especially considering I’m buying a used non-current unit. I have access to incredible techs and would never send anything back to Viva directly for repair. With this in mind, I’d be much more interested in someone posting something that is actually helpful in answering my question. Thanks.
Jond:

Wow, I was interested in this preamplifier and I thought you taking the time out of schedule to mention possible pitfalls was incredibly helpful and thoughtful.
Jond - I want to echo audiofun here. I never intended that you were not being helpful. I think you were trying to be very helpful. It just didn’t answer my question.